head to head · open source
calibre vs hammer-editor
calibre has 25,923 GitHub stars, 2,690 forks, 6 open issues and last shipped yesterday. hammer-editor has 744 stars, 42 forks, 54 open issues and last shipped 2 days ago. calibre leads on adoption by 3,384% (25,923 vs 744 stars). calibre is written in Python under GPL-3.0; hammer-editor is written in Kotlin under MIT. calibre has attracted 10% as many forks as stars, hammer-editor 6%. calibre was the more recently maintained of the two, and both are self-hostable with no licence fee.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| calibre | hammer-editor | |
|---|---|---|
| GitHub stars | ★ 26K | ★ 744 |
| License | GPL-3.0 | MIT |
| Written in | Python | Kotlin |
| Last push | 2026-09-17 | 2026-09-16 |
| Forks | ⑂ 2.7K | ⑂ 42 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick calibre if
- You weight community size — 26K stars and counting
- You want the GPL-3.0 license terms
- Your stack matches Python
- You value the larger contributor base for long-term maintenance
pick hammer-editor if
- You want the hammer-editor feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches Kotlin
- You evaluated both and hammer-editor fits your workflow better
About calibre
calibre is the official source code repository for the calibre e book manager, an open source application written in Python and released under GPL 3.0. It lives in the content and publishing ecosystem as a desktop tool for books, and it is cross platform, running on Linux, Windows and macOS. The project has been hosted on GitHub for roughly thirteen years, carries about 25,900 stars and 2,683 forks, and its home on the web is calibre ebook.com, where an About page and a screenshots page document it further.
read the full calibre overview →
About hammer-editor
Hammer is a free, open source, local first story editor for writers, built in Kotlin with Compose Multiplatform and shipped for Android, iOS, Windows, Linux and macOS, so a single draft stays with its author across phone and desktop.
read the full hammer-editor overview →
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Frequently asked questions
Is calibre or hammer-editor more popular?
calibre has 25,923 GitHub stars and hammer-editor has 744. calibre has the larger community by that measure.
Are calibre and hammer-editor free?
Both are open source. calibre is licensed under GPL-3.0 and hammer-editor under MIT. Neither carries a licence fee.
What is the difference between calibre and hammer-editor?
calibre is written in Python and hammer-editor in Kotlin. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, calibre or hammer-editor?
Choose calibre if you want the larger community (25,923 stars) or its GPL-3.0 licence terms. Choose hammer-editor if its feature set, stack or MIT licence fits better. Both are self-hostable.