Citadel vs Group-Office
A side-by-side comparison of two self-hosted groupware options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Citadel | Group-Office |
|---|---|---|
| Deploy effort | Read-the-docs project | Under-an-hour setup |
| Category | Groupware | Groupware |
| License | GPL-3.0 | AGPL-3.0 |
| Language | C | PHP |
| Setup difficulty | Medium | Medium |
| Min. RAM | 512 MB | 1,024 MB |
| Deployment | bare-metal, source | docker, bare-metal |
| GitHub stars | ★ 100 | ★ 279 |
| First released | 1987 | 2003 |
| Replaces | Microsoft Exchange, Microsoft 365 | Microsoft 365, Google Workspace |
What are Citadel and Group-Office?
Citadel
Citadel is a mature, all-in-one collaboration suite that integrates email, calendaring, address books, instant messaging, and bulletin boards. It is designed for easy installation and minimal maintenance.
- Integrated mail and calendar
- Built-in groupware web client
- Instant messaging and forums
- Easy installer
Group-Office
Group-Office is a PHP-based groupware suite that bundles email, calendar, contacts, file sharing, and project management. The community edition is open source and self-hostable.
- Email, calendar and contacts
- ActiveSync and CalDAV support
- Project and document management
- Modular and extensible
Citadel vs Group-Office: key differences
Citadel is written in C, while Group-Office is built with PHP. Licensing differs — GPL-3.0 for Citadel versus AGPL-3.0 for Group-Office. Citadel is the lighter option, starting around 512 MB of RAM against 1,024 MB for Group-Office. Citadel is the more established project (first released 1987), while Group-Office arrived in 2003. Group-Office has the considerably larger community, at 279 GitHub stars versus 100. Group-Office lists first-class Docker deployment; Citadel does not.
Why pick each one
Choose Citadel if…
- Single-package setup
- Low resource needs
Watch out for
- Niche project
- Old-fashioned UI
Choose Group-Office if…
- Released under the AGPL-3.0 license
- First-class Docker support for quick deployment
- Written in PHP
Watch out for
- Some modules are commercial
- Dated user interface
Frequently asked questions
Is Citadel or Group-Office better?
Neither is universally better. Group-Office has the larger community; both share a medium setup difficulty, so the decision comes down to features and licensing.
Are Citadel and Group-Office free and open-source?
Yes. Citadel is licensed under GPL-3.0 and Group-Office under AGPL-3.0. Both can be self-hosted at no software cost.
Can I run Citadel and Group-Office with Docker?
Citadel: check the project docs for container support. Group-Office: yes.
Which is lighter on resources, Citadel or Group-Office?
Citadel has the smaller minimum footprint at 512 MB of RAM, compared to about 1,024 MB for Group-Office. Real-world usage depends on library size, user count, and enabled features.