head to head · open source
Signal vs pki
Signal has 29,361 GitHub stars, 6,891 forks, 498 open issues and last shipped yesterday. pki has 509 stars, 162 forks, 46 open issues and last shipped yesterday. Signal leads on adoption by 5,668% (29,361 vs 509 stars). Signal is written in Kotlin under AGPL-3.0; pki is written in Java under GPL-2.0. Signal has attracted 23% as many forks as stars, pki 32%. Signal 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
| Signal | pki | |
|---|---|---|
| GitHub stars | ★ 29K | ★ 509 |
| License | AGPL-3.0 | GPL-2.0 |
| Written in | Kotlin | Java |
| Last push | 2026-09-18 | 2026-09-18 |
| Forks | ⑂ 6.9K | ⑂ 162 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick Signal if
- You weight community size — 29K stars and counting
- You want the AGPL-3.0 license terms
- Your stack matches Kotlin
- You value the larger contributor base for long-term maintenance
pick pki if
- You want the pki feature set and don't need the biggest community
- You prefer the GPL-2.0 license terms
- Your stack matches Java
- You evaluated both and pki fits your workflow better
About Signal
Signal Android is a secure messaging application for Android devices that delivers private communication via end to end encryption. Developed by Signal Messenger, LLC, it operates within the broader Signal ecosystem, which includes official iOS and desktop clients. The app uses mobile data or Wi Fi to send and receive encrypted messages, voice calls, and video calls without relying on traditional SMS or telephony infrastructure.
read the full Signal overview →
About pki
Dogtag PKI is an enterprise class open source Certificate Authority suite, written in Java and licensed under GPL 2.0, for administrators who need to run their own certificate lifecycle infrastructure rather than buy it as a hosted service.
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Frequently asked questions
Is Signal or pki more popular?
Signal has 29,361 GitHub stars and pki has 509. Signal has the larger community by that measure.
Are Signal and pki free?
Both are open source. Signal is licensed under AGPL-3.0 and pki under GPL-2.0. Neither carries a licence fee.
What is the difference between Signal and pki?
Signal is written in Kotlin and pki 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, Signal or pki?
Choose Signal if you want the larger community (29,361 stars) or its AGPL-3.0 licence terms. Choose pki if its feature set, stack or GPL-2.0 licence fits better. Both are self-hostable.