Citadel vs Kopano Groupware Core
A side-by-side comparison of two self-hosted groupware options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Citadel | Kopano Groupware Core |
|---|---|---|
| Deploy effort | Read-the-docs project | Under-an-hour setup |
| Category | Groupware | Groupware |
| License | GPL-3.0 | AGPL-3.0 |
| Language | C | C++ |
| Setup difficulty | Medium | Hard |
| Min. RAM | 512 MB | 2,048 MB |
| Deployment | bare-metal, source | docker, bare-metal |
| GitHub stars | ★ 100 | ★ 60 |
| First released | 1987 | 2016 |
| Replaces | Microsoft Exchange, Microsoft 365 | Microsoft Exchange |
What are Citadel and Kopano Groupware Core?
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
Kopano Groupware Core
Kopano Groupware Core is an open-source collaboration suite providing email, calendaring, and contacts with MAPI compatibility. It serves as the foundation of a self-hosted Exchange alternative.
- MAPI-based architecture
- Shared calendars and folders
- ActiveSync via Z-Push
- Web-based email client
Citadel vs Kopano Groupware Core: key differences
Citadel is written in C, while Kopano Groupware Core is built with C++. Licensing differs — GPL-3.0 for Citadel versus AGPL-3.0 for Kopano Groupware Core. Citadel is the lighter option, starting around 512 MB of RAM against 2,048 MB for Kopano Groupware Core. Citadel is the more established project (first released 1987), while Kopano Groupware Core arrived in 2016. Kopano Groupware Core 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 Kopano Groupware Core if…
- Released under the AGPL-3.0 license
- First-class Docker support for quick deployment
- Written in C++
Watch out for
- Complex multi-component setup
- Slower recent development
Frequently asked questions
Is Citadel or Kopano Groupware Core better?
Citadel is the stronger all-round pick: it has both the larger community and the simpler medium setup. Consider Kopano Groupware Core if its specific feature set fits your needs better.
Are Citadel and Kopano Groupware Core free and open-source?
Yes. Citadel is licensed under GPL-3.0 and Kopano Groupware Core under AGPL-3.0. Both can be self-hosted at no software cost.
Can I run Citadel and Kopano Groupware Core with Docker?
Citadel: check the project docs for container support. Kopano Groupware Core: yes.
Which is lighter on resources, Citadel or Kopano Groupware Core?
Citadel has the smaller minimum footprint at 512 MB of RAM, compared to about 2,048 MB for Kopano Groupware Core. Real-world usage depends on library size, user count, and enabled features.