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Technology Digital MediaTop 10 Best Opensource Calendar Software of 2026
How we ranked these tools
Core product claims cross-referenced against official documentation, changelogs, and independent technical reviews.
Analyzed video reviews and hundreds of written evaluations to capture real-world user experiences with each tool.
AI persona simulations modeled how different user types would experience each tool across common use cases and workflows.
Final rankings reviewed and approved by our editorial team with authority to override AI-generated scores based on domain expertise.
Score: Features 40% · Ease 30% · Value 30%
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Editor picks
Three standouts derived from this page's comparison data when the live shortlist is not available yet — best choice first, then two strong alternatives.
Nextcloud Calendar
Deep integration with the Nextcloud ecosystem, allowing calendars to link directly with files, tasks (Deck), contacts, and chat (Talk) for unified workflows.
Built for privacy-conscious individuals, teams, and organizations seeking a self-hosted calendar with deep integration into a full open-source productivity suite..
SOGo
Native ActiveSync support for full Exchange protocol compatibility on iOS/Android without bridges
Built for organizations and teams needing a free, scalable shared calendar server with Exchange-like mobile sync..
Zimbra
Integrated group calendaring with email and shared briefcase for seamless team scheduling and document collaboration
Built for mid-to-large organizations needing a free, self-hosted groupware solution with strong calendar capabilities as part of a full collaboration platform..
Comparison Table
Open-source calendar software provides versatile options for managing schedules, and with tools like Nextcloud Calendar, SOGo, Zimbra, Radicale, Xandikos, and more, selecting the ideal solution demands clarity on features and functionality. This comparison table simplifies the process by outlining key attributes, integration strengths, and user-friendliness, enabling readers to identify the tool that best suits their operational or personal needs.
| # | Tool | Category | Overall | Features | Ease of Use | Value |
|---|---|---|---|---|---|---|
| 1 | Nextcloud Calendar Feature-rich self-hosted calendar application with event sharing, recurring events, tasks, and CalDAV sync for individuals and teams. | other | 9.4/10 | 9.6/10 | 8.5/10 | 10/10 |
| 2 | SOGo Scalable open-source groupware server offering shared calendars, contacts, and email with ActiveSync, CalDAV, and WebDAV support. | other | 9.0/10 | 9.5/10 | 7.5/10 | 10/10 |
| 3 | Zimbra Comprehensive open-source collaboration suite providing advanced calendaring, scheduling, and resource booking alongside email and file sharing. | other | 8.2/10 | 9.0/10 | 6.5/10 | 9.5/10 |
| 4 | Radicale Lightweight CalDAV and CardDAV server enabling simple calendar and contact synchronization without a database. | other | 8.4/10 | 7.6/10 | 8.7/10 | 10/10 |
| 5 | Xandikos Modern, standards-compliant CalDAV and CardDAV server built in Python for efficient calendar and address book sharing. | other | 8.2/10 | 7.8/10 | 7.0/10 | 9.5/10 |
| 6 | Horde Groupware Modular open-source web-based groupware with integrated calendar, event management, and sharing capabilities. | other | 7.2/10 | 8.5/10 | 5.8/10 | 9.5/10 |
| 7 | EGroupware Flexible open-source groupware platform featuring shared calendars, resource booking, and integration with other productivity tools. | other | 7.4/10 | 8.2/10 | 6.5/10 | 9.5/10 |
| 8 | Tine 2.0 Extensible open-source groupware with robust calendar features, recurring events, and multi-user collaboration. | other | 8.1/10 | 8.7/10 | 7.2/10 | 9.4/10 |
| 9 | DAViCal PHP-based CalDAV server designed for free/busy time sharing and group calendar management using a SQL database. | other | 7.2/10 | 8.0/10 | 5.8/10 | 9.5/10 |
| 10 | Baïkal Minimalist CalDAV and CardDAV server providing basic calendar synchronization and an intuitive web admin interface. | other | 7.3/10 | 6.5/10 | 8.2/10 | 9.5/10 |
Feature-rich self-hosted calendar application with event sharing, recurring events, tasks, and CalDAV sync for individuals and teams.
Scalable open-source groupware server offering shared calendars, contacts, and email with ActiveSync, CalDAV, and WebDAV support.
Comprehensive open-source collaboration suite providing advanced calendaring, scheduling, and resource booking alongside email and file sharing.
Lightweight CalDAV and CardDAV server enabling simple calendar and contact synchronization without a database.
Modern, standards-compliant CalDAV and CardDAV server built in Python for efficient calendar and address book sharing.
Modular open-source web-based groupware with integrated calendar, event management, and sharing capabilities.
Flexible open-source groupware platform featuring shared calendars, resource booking, and integration with other productivity tools.
Extensible open-source groupware with robust calendar features, recurring events, and multi-user collaboration.
PHP-based CalDAV server designed for free/busy time sharing and group calendar management using a SQL database.
Minimalist CalDAV and CardDAV server providing basic calendar synchronization and an intuitive web admin interface.
Nextcloud Calendar
otherFeature-rich self-hosted calendar application with event sharing, recurring events, tasks, and CalDAV sync for individuals and teams.
Deep integration with the Nextcloud ecosystem, allowing calendars to link directly with files, tasks (Deck), contacts, and chat (Talk) for unified workflows.
Nextcloud Calendar is a robust, open-source calendar application embedded within the Nextcloud self-hosted collaboration platform, enabling users to create, share, and manage events, appointments, and resources with full data sovereignty. It supports CalDAV/CardDAV synchronization across desktop, web, and mobile clients, along with advanced features like recurring events, invitations, attachments, and resource booking. As part of the modular Nextcloud ecosystem, it integrates seamlessly with tasks, contacts, files, and communication tools for a comprehensive productivity experience.
Pros
- Fully open-source (AGPL) with complete self-hosting control and privacy
- Rich feature set including CalDAV sync, resource booking, and ecosystem integrations
- No licensing costs; scalable from personal to enterprise use
Cons
- Requires server setup and ongoing maintenance, not plug-and-play
- Performance can degrade with large-scale deployments without optimization
- Web UI, while functional, lags behind proprietary apps in polish
Best For
Privacy-conscious individuals, teams, and organizations seeking a self-hosted calendar with deep integration into a full open-source productivity suite.
SOGo
otherScalable open-source groupware server offering shared calendars, contacts, and email with ActiveSync, CalDAV, and WebDAV support.
Native ActiveSync support for full Exchange protocol compatibility on iOS/Android without bridges
SOGo is a robust open-source groupware server featuring shared calendars, contacts, tasks, and email integration, with strong emphasis on calendar synchronization via CalDAV, CardDAV, and ActiveSync protocols. It supports multi-user calendar sharing, resource booking, and recurring events, making it suitable for teams and enterprises. The web-based interface provides easy access without needing desktop clients, while ensuring compatibility with major calendar apps like Outlook, iCal, and mobile devices.
Pros
- Excellent multi-protocol support (CalDAV, CardDAV, ActiveSync) for seamless cross-device sync
- Scalable for enterprise use with high performance in shared calendar environments
- Integrated groupware features including tasks and resource management
Cons
- Server setup requires Linux sysadmin knowledge and dependencies like Postfix/Dovecot
- Web UI is functional but lacks modern polish compared to newer alternatives
- Limited built-in video conferencing or advanced collaboration tools
Best For
Organizations and teams needing a free, scalable shared calendar server with Exchange-like mobile sync.
Zimbra
otherComprehensive open-source collaboration suite providing advanced calendaring, scheduling, and resource booking alongside email and file sharing.
Integrated group calendaring with email and shared briefcase for seamless team scheduling and document collaboration
Zimbra is an open-source collaboration suite that includes a robust calendar system integrated with email, contacts, tasks, and file sharing. It supports shared calendars, recurring events, resource booking, and standards like CalDAV and iCal for seamless synchronization with desktop and mobile clients. Designed for self-hosted deployments, it offers enterprise-grade features suitable for teams needing more than just a standalone calendar tool.
Pros
- Comprehensive calendar features with sharing, free/busy lookup, and resource management
- Deep integration with email and collaboration tools for unified workflow
- Highly scalable for large organizations with multi-tenancy support
Cons
- Complex server installation and configuration requiring Linux admin skills
- Web interface feels dated compared to modern SaaS calendars
- Limited mobile app; relies on standard protocols which may need third-party clients
Best For
Mid-to-large organizations needing a free, self-hosted groupware solution with strong calendar capabilities as part of a full collaboration platform.
Radicale
otherLightweight CalDAV and CardDAV server enabling simple calendar and contact synchronization without a database.
Database-less filesystem storage for ultimate simplicity and low overhead
Radicale is a lightweight, free, and open-source CalDAV and CardDAV server that enables sharing and synchronization of calendars and contacts across devices and clients. Written in Python, it stores data directly on the filesystem without requiring a database, making it simple to deploy. It supports multiple users, fine-grained rights management, and is compatible with standard clients like Apple Calendar, Thunderbird, Outlook, and Android/iOS apps.
Pros
- Extremely lightweight with minimal resource usage
- No database required, uses simple filesystem storage
- Standards-compliant CalDAV/CardDAV with good client compatibility
- Flexible authentication and access control options
Cons
- No built-in web administration interface
- Limited advanced features like recurring event handling quirks
- Filesystem storage can become unwieldy at very large scales
- Configuration primarily via config files, no GUI
Best For
Self-hosting enthusiasts and small teams needing a minimal, reliable CalDAV/CardDAV server without bloat.
Xandikos
otherModern, standards-compliant CalDAV and CardDAV server built in Python for efficient calendar and address book sharing.
Git repository backend for automatic versioning of calendars and contacts
Xandikos is a lightweight, open-source CalDAV and CardDAV server that enables sharing and synchronization of calendars and contacts. It uniquely stores all data in standard Git repositories, providing automatic versioning, backups, and no need for a traditional database. Designed for simplicity, it integrates seamlessly with clients like Thunderbird, Evolution, and mobile apps via standard protocols.
Pros
- Lightweight with no database required, runs efficiently on minimal hardware
- Git-based storage offers built-in versioning and easy backups
- Standards-compliant CalDAV/CardDAV for broad client compatibility
Cons
- No web-based admin interface or GUI
- Setup requires technical knowledge like config files or Docker
- Server-only; no built-in calendar client
Best For
Tech-savvy users or small teams needing a minimal, version-controlled CalDAV/CardDAV server.
Horde Groupware
otherModular open-source web-based groupware with integrated calendar, event management, and sharing capabilities.
Built-in ActiveSync support for native Exchange-like synchronization with Outlook and mobile devices
Horde Groupware is a mature open-source web-based collaboration suite featuring Kronolith, a powerful calendar application for managing events, recurring appointments, resources, and alarms. It supports advanced sharing, permissions, and synchronization via CalDAV, WebDAV, iCalendar, and ActiveSync, integrating seamlessly with other Horde modules like email (IMP) and contacts (Turba). Ideal for group environments, it enables collaborative scheduling across teams with robust access controls and mobile compatibility.
Pros
- Comprehensive calendar features including resource booking and advanced sharing
- Strong synchronization support (CalDAV, ActiveSync) for mobile and desktop clients
- Fully open-source and highly modular for customization
Cons
- Dated and clunky web interface that feels outdated
- Complex server setup requiring PHP, database, and multiple dependencies
- Steeper learning curve for non-technical users
Best For
Teams or organizations seeking a free, self-hosted groupware calendar with deep integration into email and contacts management.
EGroupware
otherFlexible open-source groupware platform featuring shared calendars, resource booking, and integration with other productivity tools.
Advanced resource booking system for managing rooms, equipment, and vehicles with conflict detection
EGroupware is a mature open-source groupware suite featuring a robust calendar module for shared scheduling, recurring events, alarms, and resource booking across teams. It supports CalDAV/CardDAV for seamless integration with clients like Thunderbird or iOS devices, and includes permissions for public/private calendars. As part of a full collaboration platform, it extends beyond calendars to email, contacts, and project management.
Pros
- Comprehensive calendar sharing and resource management with fine-grained permissions
- CalDAV/CardDAV support for broad client compatibility
- Full groupware integration at no cost
Cons
- Dated web interface feels clunky compared to modern alternatives
- Complex initial setup requiring server admin knowledge
- Limited native mobile apps; relies on third-party DAV clients
Best For
Mid-sized organizations or teams needing an all-in-one open-source groupware solution with strong calendar and resource booking capabilities.
Tine 2.0
otherExtensible open-source groupware with robust calendar features, recurring events, and multi-user collaboration.
Native ActiveSync support for seamless integration with Outlook and native mobile apps
Tine 2.0 is an open-source groupware platform featuring a comprehensive calendar system integrated with email, contacts, CRM, and project management tools. It supports CalDAV/CardDAV and ActiveSync for cross-device synchronization, shared calendars, recurring events, resource booking, and advanced permissions. Designed for enterprise use, it offers extensibility through plugins and a web-based interface for team collaboration.
Pros
- Robust calendar features including resource booking, shared calendars, and recurring events
- Excellent sync support via CalDAV, CardDAV, and ActiveSync for mobile/desktop clients
- Integrated groupware suite reduces need for multiple tools
Cons
- Complex installation and configuration requiring server admin expertise
- Dated user interface compared to modern alternatives
- Limited community support and documentation for advanced customizations
Best For
Mid-sized teams or organizations needing a self-hosted, all-in-one groupware solution with strong calendar synchronization.
DAViCal
otherPHP-based CalDAV server designed for free/busy time sharing and group calendar management using a SQL database.
Comprehensive CalDAV protocol implementation with advanced scheduling features like free/busy aggregation and invite handling
DAViCal is an open-source CalDAV and CardDAV server that enables centralized storage, sharing, and synchronization of calendars and contacts across multiple clients. It uses a PostgreSQL database backend and provides a web-based administration interface for managing users, collections, and permissions. Primarily designed as a backend service, it integrates seamlessly with standards-compliant clients like Apple iCal, Thunderbird Lightning, and Evolution, supporting features like free/busy lookups and scheduling.
Pros
- Standards-compliant CalDAV and CardDAV support for reliable syncing
- Robust permission and sharing controls for teams
- Lightweight and scalable with PostgreSQL backend
- Active community and free forever as open-source
Cons
- Complex installation requiring manual setup of PHP, Apache/Nginx, and PostgreSQL
- Outdated web interface lacking modern calendar viewing
- No built-in mobile or rich web client
- Limited documentation and support for beginners
Best For
Sysadmins or organizations needing a reliable, self-hosted CalDAV backend for integrating with existing desktop and mobile calendar clients.
Baïkal
otherMinimalist CalDAV and CardDAV server providing basic calendar synchronization and an intuitive web admin interface.
Pure focus on CalDAV/CardDAV protocol implementation for reliable, standard syncing without extraneous features.
Baïkal, from the Sabre.io project, is a lightweight open-source CalDAV and CardDAV server designed for syncing calendars, contacts, and address books across devices and clients like Apple Calendar, Thunderbird, and Android apps. It serves as a minimalistic backend without a web UI, emphasizing standards compliance for seamless integration. Users configure it via PHP on a web server with databases like SQLite or MySQL, making it suitable for self-hosting personal sync servers.
Pros
- Extremely lightweight and low-resource usage
- Full CalDAV and CardDAV standards compliance for broad client support
- Simple installation with minimal dependencies
Cons
- No built-in web interface for event management or admin tasks
- Limited features like no native sharing, tasks, or advanced querying
- Requires external clients for all calendar interactions
Best For
Tech-savvy users seeking a bare-bones, self-hosted sync server for calendars and contacts without bloat.
Conclusion
After evaluating 10 technology digital media, Nextcloud Calendar stands out as our overall top pick — it scored highest across our combined criteria of features, ease of use, and value, which is why it sits at #1 in the rankings above.
Use the comparison table and detailed reviews above to validate the fit against your own requirements before committing to a tool.
Tools reviewed
Referenced in the comparison table and product reviews above.
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