Thunderbird Appointment vs Crab Fit
A side-by-side comparison of two self-hosted calendar & contacts options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Thunderbird Appointment | Crab Fit |
|---|---|---|
| Deploy effort | Under-an-hour setup | Under-an-hour setup |
| Health score | 80 · Excellent | 58 · Fair |
| Category | Calendar & Contacts | Calendar & Contacts |
| License | MPL-2.0 | MIT |
| Language | Python | TypeScript |
| Setup difficulty | Medium | Easy |
| Min. RAM | 512 MB | 256 MB |
| Deployment | docker, source | docker |
| GitHub stars | ★ 552 | ★ 531 |
| First released | 2023 | 2020 |
| Replaces | Calendly, Doodle | When2meet, Doodle |
What are Thunderbird Appointment and Crab Fit?
Thunderbird Appointment
Thunderbird Appointment is an open-source scheduling application that lets users share availability and let others book time slots. It integrates with CalDAV calendars and is built by the Thunderbird team.
- Availability sharing
- Bookable time slots
- CalDAV integration
- Built by Thunderbird
Crab Fit
Crab Fit is an open-source scheduling tool that helps groups find a time to meet by overlaying everyone's availability. Participants mark free slots without registering, and a heatmap reveals the best overlap, similar to When2meet.
- Availability heatmap
- No registration required
- Group time-finding
Thunderbird Appointment vs Crab Fit: key differences
Thunderbird Appointment is written in Python, while Crab Fit is built with TypeScript. Licensing differs — MPL-2.0 for Thunderbird Appointment versus MIT for Crab Fit. Crab Fit is the lighter option, starting around 256 MB of RAM against 512 MB for Thunderbird Appointment. Crab Fit is the more established project (first released 2020), while Thunderbird Appointment arrived in 2023.
Why pick each one
Choose Thunderbird Appointment if…
- Released under the MPL-2.0 license
- First-class Docker support for quick deployment
- Written in Python
- Lightweight — runs in 512 MB RAM
Choose Crab Fit if…
- Released under the MIT license
- Easy to set up — beginner-friendly
- First-class Docker support for quick deployment
- Written in TypeScript
Frequently asked questions
Is Thunderbird Appointment or Crab Fit better?
Neither is universally better. Thunderbird Appointment has the larger community, while Crab Fit is simpler to set up (easy difficulty). Choose based on the comparison table above and your own setup.
Are Thunderbird Appointment and Crab Fit free and open-source?
Yes. Thunderbird Appointment is licensed under MPL-2.0 and Crab Fit under MIT. Both can be self-hosted at no software cost.
Can I run Thunderbird Appointment and Crab Fit with Docker?
Thunderbird Appointment: yes. Crab Fit: yes.
Which is lighter on resources, Thunderbird Appointment or Crab Fit?
Crab Fit has the smaller minimum footprint at 256 MB of RAM, compared to about 512 MB for Thunderbird Appointment. Real-world usage depends on library size, user count, and enabled features.