Citadel vs Kolab Groupware
A side-by-side comparison of two self-hosted groupware options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Citadel | Kolab Groupware |
|---|---|---|
| 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 | Hard |
| Min. RAM | 512 MB | 2,048 MB |
| Deployment | bare-metal, source | bare-metal, docker |
| GitHub stars | ★ 100 | ★ 200 |
| First released | 1987 | 2002 |
| Replaces | Microsoft Exchange, Microsoft 365 | Microsoft Exchange, Zimbra |
What are Citadel and Kolab Groupware?
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
Kolab Groupware
Kolab is an open-source groupware solution providing email, shared calendars, contacts, tasks, and notes. It integrates standard components like Postfix, Cyrus IMAP, and Roundcube into a coherent collaboration platform.
- Email and calendaring
- Shared address books
- ActiveSync support
- Standards based
Citadel vs Kolab Groupware: key differences
Citadel is written in C, while Kolab Groupware is built with PHP. Licensing differs — GPL-3.0 for Citadel versus AGPL-3.0 for Kolab Groupware. Citadel is the lighter option, starting around 512 MB of RAM against 2,048 MB for Kolab Groupware. Citadel is the more established project (first released 1987), while Kolab Groupware arrived in 2002. Kolab Groupware has the considerably larger community, at 200 GitHub stars versus 100. Kolab Groupware 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 Kolab Groupware if…
- Built on proven components
- Strong standards support
Watch out for
- Complex to install
- Steep operational curve
Frequently asked questions
Is Citadel or Kolab Groupware better?
Neither is universally better. Kolab Groupware has the larger community, while Citadel is simpler to set up (medium difficulty). Choose based on the comparison table above and your own setup.
Are Citadel and Kolab Groupware free and open-source?
Yes. Citadel is licensed under GPL-3.0 and Kolab Groupware under AGPL-3.0. Both can be self-hosted at no software cost.
Can I run Citadel and Kolab Groupware with Docker?
Citadel: check the project docs for container support. Kolab Groupware: yes.
Which is lighter on resources, Citadel or Kolab Groupware?
Citadel has the smaller minimum footprint at 512 MB of RAM, compared to about 2,048 MB for Kolab Groupware. Real-world usage depends on library size, user count, and enabled features.