Signal's server[1] and client source code[2,3,4] has been publicly available for many years and are even licensed under the (A)GPL-3.0 (with an exception to all

Signal's server[1] and client source code[2,3,4] has been publicly available for many years and are even licensed under the (A)GPL-3.0 (with an exception to allow distribution via Google Play and the Apple App Store). I don't know where you got the impression this wasn't the case. An earlier VOIP product of theirs (RedPhone) had a proprietary server implementation, but ever since the feature was added to Signal proper it has been free software. [1]: https://github.com/signalapp/Signal-Server https://github.com/signalapp/Signal-Server [2]: https://github.com/signalapp/Signal-Android https://github.com/signalapp/Signal-Android [3]: https://github.com/signalapp/Signal-iOS https://github.com/signalapp/Signal-iOS [4]: https://github.com/signalapp/Signal-Desktop https://github.com/signalapp/Signal-Desktop