head to head · open source
Cal.com vs ical4j
Cal.com has 48,529 GitHub stars, 15,154 forks, 1,432 open issues and last shipped 4 days ago. ical4j has 837 stars, 218 forks, 162 open issues and last shipped 29 days ago. Cal.com leads on adoption by 5,698% (48,529 vs 837 stars). Cal.com is written in TypeScript under MIT; ical4j is written in Java under BSD-3-Clause. Cal.com has attracted 31% as many forks as stars, ical4j 26%. Cal.com 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
| Cal.com | ical4j | |
|---|---|---|
| GitHub stars | ★ 49K | ★ 837 |
| License | MIT | BSD-3-Clause |
| Written in | TypeScript | Java |
| Last push | 2026-09-14 | 2026-08-20 |
| Forks | ⑂ 15K | ⑂ 218 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick Cal.com if
- You weight community size — 49K stars and counting
- You want the MIT license terms
- Your stack matches TypeScript
- You value the larger contributor base for long-term maintenance
pick ical4j if
- You want the ical4j feature set and don't need the biggest community
- You prefer the BSD-3-Clause license terms
- Your stack matches Java
- You evaluated both and ical4j fits your workflow better
About Cal.com
Cal.diy is a fully open source, community maintained fork of Cal.com, stripped of all enterprise and commercial features. It provides a self hosted scheduling platform built on the T3 stack (Next.js, tRPC, Prisma, Tailwind CSS, Zod), licensed under MIT with no proprietary code or license keys required.
read the full Cal.com overview →
About ical4j
iCal4j is a BSD 3 Clause licensed Java library that reads and writes iCalendar data streams and exposes them as an object model, built for Java developers who need to handle calendar data such as events, appointments and to do lists inside their own applications.
read the full ical4j overview →
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Frequently asked questions
Is Cal.com or ical4j more popular?
Cal.com has 48,529 GitHub stars and ical4j has 837. Cal.com has the larger community by that measure.
Are Cal.com and ical4j free?
Both are open source. Cal.com is licensed under MIT and ical4j under BSD-3-Clause. Neither carries a licence fee.
What is the difference between Cal.com and ical4j?
Cal.com is written in TypeScript and ical4j in Java. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, Cal.com or ical4j?
Choose Cal.com if you want the larger community (48,529 stars) or its MIT licence terms. Choose ical4j if its feature set, stack or BSD-3-Clause licence fits better. Both are self-hostable.