Best Self Hosted Alternatives to Proton Calendar

Nextcloud is an open-source content collaboration platform that provides file synchronization, sharing, and integrated groupware. It combines file storage, real-time document collaboration, chat/voice/video, calendars and contacts under a single extensible platform.

Key Features

• File sync & share with web, desktop and mobile clients; WebDAV support for native mounts and third-party clients
• Real-time collaborative editing with Nextcloud Office (LibreOffice-based online editing)
• Private communications via Nextcloud Talk: browser and mobile chat, audio/video conferencing, screen sharing and SIP integration
• Groupware: Calendar (CalDAV), Contacts (CardDAV) and integrated mail features
• Nextcloud Assistant: integrated/local AI features for summarization, content generation and data-aware queries (platform-integrated)
• Automation and workflow tools (Flow) plus structured-data app (Nextcloud Tables) and Open Collaboration Services APIs for integrations
• Storage and backend flexibility: support for object stores (S3-compatible/MinIO/OpenStack Swift), SMB/CIFS, local filesystem and external storage mounts
• Scalability and performance options: multiple database backends (MySQL/MariaDB/PostgreSQL/SQLite), caching/file-locking with Redis or Memcached, APCu for local cache
• Extensible apps ecosystem and enterprise add-ons for auditing, access control, compliance and identity integrations

Use Cases

• Secure enterprise file sync, internal collaboration and compliance-focused deployments for organizations needing data control
• Education and public-sector deployments requiring granular access control, audit trails and privacy-preserving collaboration
• Service providers and hosters offering branded/cloud storage and collaboration services built on a customizable platform

Limitations and Considerations

• Production-scale deployments require careful configuration (database selection, caching, file-locking). SQLite is only suitable for testing or very small installs.
• Some advanced capabilities (distributed scaling, object-storage primary setups, enterprise-grade support and specific integrations) require additional infrastructure, configuration, or commercial Enterprise services.
• Performance can degrade if many heavy third-party apps are enabled or if recommended caching (e.g., Redis) is not configured; upgrades and maintenance need planning for large installations.

Nextcloud provides a comprehensive, extensible platform for organizations and individuals who need control over their collaboration stack. It balances a broad feature set with modularity so deployments can be tailored to small setups or large, regulated environments.

Radicale is a lightweight CalDAV and CardDAV server for syncing calendars, to-do lists, and contacts with a wide range of client applications. It focuses on simple deployment and straightforward storage, keeping data on the filesystem in a readable folder structure.

Key Features

• CalDAV and CardDAV support for calendars, tasks, journals, and contacts
• HTTP-based access compatible with many desktop and mobile DAV clients
• Filesystem storage with a simple folder layout (no database required)
• Authentication to restrict access to collections
• TLS support for encrypted connections
• Plugin system to extend and customize behavior

Use Cases

• Self-hosted calendar and contact sync for personal or family use
• Shared team calendars and address books for small groups
• Lightweight DAV backend for apps and devices that support CalDAV/CardDAV

Limitations and Considerations

• Filesystem-based storage may be less suitable than a database for very large, high-concurrency deployments

Radicale is a solid choice when you want standards-based DAV syncing with minimal operational overhead. Its simple storage model and extensibility make it practical for small to medium deployments needing reliable calendar and contact synchronization.

Baïkal is a lightweight CalDAV and CardDAV server for hosting calendars and contacts. It provides a web-based administrative interface to manage users, address books, and calendars, while relying on the sabre/dav DAV stack.

Key Features

• CalDAV and CardDAV server for calendar and contact synchronization
• Web interface for managing users, calendars, and address books
• Storage backend support for MySQL and SQLite
• Broad client compatibility with common DAV-capable apps (desktop and mobile)
• Designed to be simple to install on a basic PHP-capable web server

Use Cases

• Self-managed calendar and contact sync for individuals and families
• Small organizations needing DAV services without a full groupware suite
• Central DAV backend for multiple clients (mobile, desktop, and web)

Limitations and Considerations

• Focused on DAV sync and admin management; it is not a full email/groupware suite

Baïkal is a solid choice when you need standards-based CalDAV/CardDAV synchronization with minimal operational complexity. Its lightweight footprint and simple storage options make it well-suited for small deployments that prioritize interoperability and privacy.

NextcloudPi is an open-source project that provides a ready-to-use Nextcloud appliance image, installer scripts and a management interface for single-board computers, virtual machines and containers. It bundles Nextcloud with system-level tooling to simplify installation, security hardening, backups and ongoing maintenance.

Key Features

• Prebuilt images and installers for Raspberry Pi, Odroid, Rock64, Armbian boards, VMs and LXD/LXC/Proxmox containers
• Nextcloud instance preinstalled and preconfigured with sane defaults
• Apache webserver with HTTP/2, PHP runtime and PHP OPcache/APCu for performance
• MariaDB database backend with Redis memory cache support
• ncp-config text UI and a web management panel (admin interface on HTTPS port 4443)
• Setup wizard and automated tasks for easy first-run configuration
• Automatic security updates, Let’s Encrypt certificate automation and Fail2Ban/UFW firewall integration
• Mail support via Postfix and optional ModSecurity web application firewall
• File-serving extras: Samba and NFS support, USB automount and scheduled rsync
• Filesystem and backup tools: BTRFS support with snapshots, automatic snapshot sync and nc-backup/restore utilities
• System monitoring and hardening: SMART drive checks, ZRAM, Lynis/Debsecan security audits

Use Cases

• Home or small-office private cloud: host files, calendars and contacts for a household or small team
• Edge/embedded deployments: quickly convert single-board computers into a managed Nextcloud server for remote sites
• Teaching and testing: experiment with Nextcloud, backups, snapshots and container/VM deployments in labs

Limitations and Considerations

• The recommended one-line installer assumes a clean Debian installation and currently provides no automatic rollback mechanism; take backups before using the installer
• The Docker variant has been discontinued for the project; primary supported delivery is OS images, LXC/LXD or the installer script
• Hardware support and performance vary by board and configuration; larger production deployments require appropriate CPU/RAM/storage sizing

NextcloudPi provides a compact, opinionated package to run a full Nextcloud stack on low-cost hardware or containers, with focused management tooling and backup features. It is best suited for personal, small-team and edge deployments where ease of setup and maintenance are priorities.

SOGo is a fast, scalable groupware (collaboration) server that provides webmail, calendars, and address books through a modern web interface and open protocols. It is designed to sit alongside existing mail infrastructure and give users a unified experience across desktop and mobile clients.

Key Features

• AJAX-based web interface for mail, calendars, and contacts
• Standards-based interoperability with existing systems via IMAP, CalDAV, and CardDAV
• Mobile synchronization support via Microsoft ActiveSync
• Resource sharing, delegation, and permission handling for calendars and address books
• Works with many native clients without requiring plugins (depending on client capabilities)

Use Cases

• Provide a webmail and groupware frontend on top of an existing IMAP mail server
• Replace proprietary groupware with an open-standards collaboration server for organizations
• Offer shared calendars/contacts with permission management for teams and communities

Limitations and Considerations

• Requires integration with external mail services (for example IMAP/SMTP servers) rather than being a complete mail server by itself

SOGo is a strong fit for deployments that prioritize open standards, scalability, and broad client compatibility. It can be used as a central collaboration layer to provide consistent mail, calendar, and contact access across many devices and clients.

EteSync is a privacy-focused synchronization service built around zero-knowledge, end-to-end encryption, designed for syncing personal information such as calendars, contacts, tasks, and notes. The self-hostable server component (Etebase Server, formerly referred to as EteSync 2.0) provides the backend that EteSync clients connect to.

Key Features

• Zero-knowledge end-to-end encryption, so the server cannot read user data
• Sync backend for calendars, contacts, tasks, and notes via EteSync clients
• Encrypted, tamper-resistant change journal for history, review, and replay of changes
• Django-based administration for managing users and server configuration
• Supports reverse-proxy deployments and production setups with TLS termination

Use Cases

• Privately sync contacts and calendars across mobile and desktop devices without exposing data to the server operator
• Run a personal or family sync service with full control over storage and backups
• Maintain an auditable history of changes to synced data for recovery and rollback

Limitations and Considerations

• Requires compatible EteSync/Etebase client applications; it is not a generic CalDAV/CardDAV server
• Production deployments need careful TLS and reverse-proxy configuration to preserve correct host headers

EteSync is a solid choice for users who want modern encrypted synchronization with strong privacy guarantees. Self-hosting the Etebase Server provides full data ownership while keeping the convenience of multi-device sync through supported clients.

sabre/dav is a widely used PHP framework for implementing WebDAV, CalDAV, and CardDAV servers. It provides the core protocol handling and extensible building blocks needed to add file, calendar, and address book sync capabilities to PHP applications.

Key Features

• WebDAV server framework for file storage, synchronization, and remote authoring
• CalDAV support for calendar storage and scheduling workflows
• CardDAV support for address books and contact synchronization
• Extensible architecture with plugins, authentication hooks, and custom backends
• Designed to integrate into existing PHP applications and infrastructures

Use Cases

• Add WebDAV file access to a PHP application or custom storage backend
• Provide CalDAV/CardDAV endpoints for syncing calendars and contacts to clients
• Build groupware or collaboration products that need standards-based sync

sabre/dav is best suited when you need a standards-compliant DAV implementation with flexibility to connect to your own data models and storage layers, while keeping protocol complexity out of your application logic.

FluidCalendar is an open-source calendar and task management application focused on intelligent scheduling. It helps plan tasks into available time slots while integrating with external calendar providers for a consolidated view of your schedule.

Key Features

• Intelligent task scheduling to place tasks into available time blocks based on preferences
• Calendar management UI with time-blocking style views
• Integrations with Google Calendar and Microsoft Outlook (via OAuth)
• Optional CalDAV integration for additional calendar providers
• Configurable system settings and environment-based configuration
• Container-friendly deployment with a bundled PostgreSQL setup

Use Cases

• Personal time-blocking and automatic planning of daily tasks
• Combining multiple calendars (work and personal) into one scheduling workflow
• Teams or individuals who want a self-controlled alternative to proprietary smart scheduling tools

Limitations and Considerations

• The project is in active development and may be buggy or incomplete, so it may not be suitable for production use yet
• Some features may differ between the open-source edition and the hosted SaaS offering

FluidCalendar is a good fit for users who want an open, customizable scheduling workflow with modern calendar UI and external calendar synchronization. It is especially useful for experimentation and iterative improvement while the project matures.

Cyrus IMAP is a long-running, production-grade server for hosting email along with contacts and calendars. It focuses on security and scalability by keeping mailboxes in server-managed storage and exposing access via standard protocols.

Key Features

• IMAP and JMAP support for mailbox access
• CalDAV and CardDAV support for calendars and contacts
• POP3, NNTP, and WebDAV protocol support (deployment-dependent)
• Mailbox ACLs and quota management for multi-user environments
• Replication and “Murder” aggregation for large and distributed setups
• Flexible server-side mail filtering via Sieve
• Search capabilities (with optional components depending on build)
• Extensive authentication options via Cyrus SASL
• Integrations for antivirus and antispam toolkits
• Deliverability-related support for SPF, DKIM, and DMARC (typically via integration with surrounding mail stack)

Use Cases

• Hosting IMAP/JMAP mailboxes for an organization where users do not need shell access
• Providing CalDAV/CardDAV services for groupware-style deployments
• Building a scalable mail backend for service providers or large enterprises

Limitations and Considerations

• A full email system typically requires integration with an MTA and additional components for webmail, spam filtering, and DKIM signing

Cyrus IMAP is well-suited to administrators who need a robust standards-based messaging platform with strong performance characteristics and operational controls. It is commonly used in demanding environments where scalability, manageability, and protocol support are priorities.

Davis is a feature-rich DAV server and web administration interface built on sabre/dav. It provides CalDAV and CardDAV services (and optional WebDAV) along with a modern, responsive dashboard for managing users, calendars, and address books.

Key Features

• CalDAV, CardDAV, and optional WebDAV support via sabre/dav
• Web admin dashboard for user management, calendar and address book creation, and sharing
• Public calendars accessible via an unguessable link (when enabled)
• Automatic birthday calendar generated from contact birthdates
• Multiple authentication methods: HTTP Basic, IMAP, or LDAP (via external providers)
• Container-friendly deployment with Docker images and sample docker-compose setup

Use Cases

• Self-hosted calendar and contacts server for personal, family, or small-team use
• Replace or modernize legacy Baïkal-style DAV setups with a maintained admin UI
• Provide shared calendars (including scheduling/invites, depending on client support)

Limitations and Considerations

• Some features depend on DAV client capabilities (for example scheduling, notifications, subscriptions)
• PostgreSQL and SQLite are supported but noted as less extensively tested than MySQL/MariaDB

Davis is well-suited for operators who want a standards-based CalDAV/CardDAV server with an approachable administration experience. It combines a modern Symfony application with sabre/dav to deliver a practical, maintainable groupware foundation.

Xandikos is a lightweight CalDAV/CardDAV server written in Python that stores calendar and contact collections in a backing Git repository. It provides WebDAV-based access to calendars (CalDAV) and address books (CardDAV) while keeping automatic history via Git commits.

Key Features

• Implements CalDAV and CardDAV server functionality with WebDAV foundations and synchronization extensions for efficient client sync.
• Uses a Git repository as the storage backend so calendar and contact changes are recorded as Git history, enabling versioning and simple backups.
• Written in Python and using Jinja2 for templating; dependencies include Dulwich, icalendar, and defusedxml (as noted in project documentation).
• Supports key WebDAV/CalDAV RFCs (CalDAV and CardDAV fully implemented; core WebDAV largely implemented with some omissions such as LOCK operations and partial support for versioning extensions).
• Designed to run under WSGI/uWSGI and can be fronted by common web servers for authentication and production deployment.
• Tested interoperability with common CalDAV/CardDAV clients and synchronization tools.

Use Cases

• Personal or small-team calendar and contact hosting where Git-backed history and simple deployment are desired.
• Keeping an auditable history of calendar/contact changes for backups or forensic inspection.
• Integrating CalDAV/CardDAV access into environments where storing data as files in Git repositories fits existing workflows.

Limitations and Considerations

• No multi-user account management; primarily intended for single-user or shared-repo setups where per-user isolation is not required.
• Does not implement CalDAV scheduling extensions and lacks some WebDAV features (for example, LOCK operations are not implemented and versioning extensions are only partially supported).

Xandikos is a pragmatic, file-oriented CalDAV/CardDAV server focused on simplicity and Git-backed history. It is suitable when Git-based storage and straightforward CalDAV/CardDAV compatibility are more important than full multi-user or advanced CalDAV scheduling features.

Manage My Damn Life (MMDL) is a self-hosted web frontend for managing CalDAV tasks and calendar events. It provides a desktop-first UI for VTODO and VEVENT management, multi-user and multi-CalDAV account support, and several task-focused views.

Key Features

• CalDAV client UI for tasks (VTODO) and calendar events (VEVENT) with fields like due, status, description and recurrence.
• Supports sub-tasks, task filters, multiple CalDAV accounts and multiple user accounts.
• Multiple views: list view, calendar view and a Gantt-like view for task scheduling and timeline visualization.
• Desktop-first responsive-ish interface focused on web use; includes screenshots and a demo image in docs.
• Open source codebase with containerized deployment artifacts (Dockerfile and docker-compose samples) and migration tooling.
• Built using a modern JavaScript/TypeScript stack with testing configuration included.

Use Cases

• Self-hosted teams or individuals who run CalDAV servers (Nextcloud, Baïkal, Radicale) and want a browser-based task/calendar frontend.
• Project planning where users need list, filterable task views and a Gantt-style timeline alongside calendar events.
• Users who prefer open source, locally hosted tooling and want to integrate multiple CalDAV accounts into a single UI.

Limitations and Considerations

• As documented in the project docs, CalDAV authentication currently supports basic authentication; OAuth for CalDAV accounts is not supported for full CalDAV authentication workflows.
• The project is marked beta; users should be careful when connecting production data and expect occasional rough edges or missing fields compared to full RFC 5545 coverage.

Manage My Damn Life is focused on providing a pragmatic, open source web UI for CalDAV-hosted tasks and calendars. It is suitable for self-hosting and local deployment using the repository and container artifacts, and development documentation is provided with the source code.

EGroupware is a browser-based, open-source groupware suite for teams and organisations, providing calendars, contacts, email, file management, tasks and project tools accessible from desktop and mobile browsers. It is developed and maintained by the EGroupware project and available as cloud packages or on-premises installations. (egroupware.org)

Key Features

• Unified online office: calendar, address book, tasks, projects, ticketing and integrated email client. (egroupware.org)
• Integrated online document editing via Collabora Online for collaborative editing of text, spreadsheet and presentation files. (egroupware.org)
• Modern frontend based on Web Components / Lit (notable tech change in recent releases). (egroupware.org)
• Flexible authentication and SSO options (OpenID Connect, OAuth, SAML) and LDAP/AD synchronization for user management. (github.com)
• Multiple deployment options: Linux packages, Docker containers and cloud-hosted trial packages; push/notification server and integrations for chat/video/remote-desktop. (github.com)

Use Cases

• Company intranet and team collaboration with shared calendars, tasks and project tracking. (egroupware.org)
• Secure document collaboration and editing with Collabora Online for teams avoiding desktop office installs. (egroupware.org)
• Centralised user/auth management for organisations using LDAP/AD and federated login (OpenID/OAuth/SAML). (github.com)

Limitations and Considerations

• Full feature set and recommended installation path rely on distribution packages or Docker; a manual developer clone/install can be more complicated and may miss components (push-server, integrations). (github.com)

EGroupware is a mature, extensible groupware platform aimed at organisations that require full data control and multiple integration points. It is actively developed with regular releases and public demos/trials available from the project. (egroupware.org)

tine is a modular, PHP-based groupware platform that provides integrated collaboration services for organizations. It bundles calendar, contacts, mail, tasks, CRM, time tracking and file management with sync protocols for common clients.

Key Features

• Unified groupware stack: calendar, address book, tasks, email client, CRM, project time tracking and file manager
• Sync protocols: CalDAV, CardDAV, WebDAV and ActiveSync for broad client compatibility
• Authentication and user management with role/permission support and licensing options
• Deployable as OCI/Docker images with support for PHP 8.1–8.3, MySQL/MariaDB and Redis backends
• Modern web UI built with JavaScript and Vue; server-side runs on PHP (php-fpm) behind Nginx or Apache
• Extensible add-on architecture and administrative tooling for operators

Use Cases

• Provide on-premises collaboration for small to medium organizations replacing cloud groupware
• Centralize CRM, email and time tracking for project billing and client management
• Synchronize calendars and contacts across mobile and desktop clients using CalDAV/CardDAV/ActiveSync

Limitations and Considerations

• Official community releases restrict free instances to five user accounts without a licence key
• Production deployments require careful planning for performance, HA and security; operators should be trained
• Some enterprise features and commercial support are available only via paid packages

tine is suitable for organizations that need a self-hosted, full-featured groupware platform with broad client compatibility and an extensible modular architecture. It is designed for administrators who can manage PHP/MySQL-based deployments and prefer on-premise control.

DAViCal is a server for calendar sharing and scheduling based on the CalDAV protocol. It stores iCalendar resources on a centralized server so multiple users and clients can collaborate on shared calendars.

Key Features

• CalDAV implementation for storing and serving iCalendar calendar data
• PostgreSQL-backed storage for calendaring resources and metadata
• Basic delegation of read/write access between users
• Concurrent multi-client access for reading and writing the same calendars over time
• Scheduling support with free/busy time display for meeting planning
• Backward-compatible WebDAV access (read-only or read-write, with caveats)

Use Cases

• Host shared team calendars compatible with common CalDAV-capable clients
• Provide calendaring for organizations that want server-side access control and delegation
• Run a central scheduling and free/busy service for coordinating meetings

Limitations and Considerations

• WebDAV fallback access is supported but not recommended compared to native CalDAV
• Deployment depends on a compatible PHP runtime and a PostgreSQL database

DAViCal is a practical choice when you need a standards-based CalDAV server with broad client interoperability and simple, database-backed management of shared calendars. It fits well for small to mid-sized deployments that prioritize compatibility and straightforward calendaring features.