head to head · open source
calibre vs substance
calibre has 26,327 GitHub stars, 2,743 forks, 6 open issues and last shipped yesterday. substance has 2,738 stars, 121 forks, 41 open issues and last shipped 7 months ago. calibre leads on adoption by 862% (26,327 vs 2,738 stars). calibre is written in Python under GPL-3.0; substance is written in JavaScript under MIT. calibre has attracted 10% as many forks as stars, substance 4%. 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 | substance | |
|---|---|---|
| GitHub stars | ★ 26K | ★ 2.7K |
| License | GPL-3.0 | MIT |
| Written in | Python | JavaScript |
| Last push | 2026-11-02 | 2026-04-02 |
| Forks | ⑂ 2.7K | ⑂ 121 |
| 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 substance if
- You want the substance feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches JavaScript
- You evaluated both and substance fits your workflow better
About calibre
calibre calibre is an e book manager. It can view, convert, edit and catalog e books in all of the major e book formats. It can also talk to e book reader devices. It can go out to the internet and fetch metadata for your books. It can download newspapers and convert them into e books for convenient reading. It is cross platform, running on Linux, Windows and macOS. For more information, see the calibre About page. Screenshots Screenshots page Usage See the User Manual. Development Setting up a development environment for calibre. A tarball of the source code for the current calibre release. Bugs Bug reports and…
read the full calibre overview →
About substance
Substance.js Substance is a JavaScript library for web based content editing. It provides building blocks for realizing custom text editors and web based publishing system. It is developed to power our online editing platform Substance. Development Install the dev dependencies. Run the dev server. Navigate to for the running the browser test suite. The test suite is rebuilt as you make changes to the source files. To run the test suite headless.
read the full substance overview →
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Frequently asked questions
Is calibre or substance more popular?
calibre has 26,327 GitHub stars and substance has 2,738. calibre has the larger community by that measure.
Are calibre and substance free?
Both are open source. calibre is licensed under GPL-3.0 and substance under MIT. Neither carries a licence fee.
What is the difference between calibre and substance?
calibre is written in Python and substance in JavaScript. 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 substance?
Choose calibre if you want the larger community (26,327 stars) or its GPL-3.0 licence terms. Choose substance if its feature set, stack or MIT licence fits better. Both are self-hostable.