Add StoneAge Messenger (#2640)

README.md

@@ -213,6 +213,7 @@ _See also: [Comparison of CalDAV and CardDAV implementations - Wikipedia](https:
 - [Shhh](https://github.com/smallwat3r/shhh) - Keep secrets out of emails or chat logs, share them using secure links with passphrase and expiration dates. `MIT` `Python`
 - [Spectrum 2](https://spectrum.im/) - Spectrum 2 is an open source instant messaging transport.  It allows users to chat together even when they are using different IM networks. ([Source Code](https://github.com/SpectrumIM/spectrum2)) `GPL-3.0` `C++`
 - [Spreed](https://www.spreed.me/) - WebRTC audio/video calls, conferencing server, and web client. ([Source Code](https://github.com/strukturag/spreed-webrtc)) `AGPL-3.0` `Go`
+- [StoneAge Messenger](https://cweb.gitlab.io/StoneAge.html) - A self-hosted Android messenger, S3-compatible storage is the only backend needed. ([Source Code](https://gitlab.com/cweb-repos/cweb-conversations), [Clients](https://f-droid.org/en/packages/com.cweb.messenger/)) `GPL-3.0` `Java`
 - [Synapse](https://matrix.org/docs/projects/server/synapse) - Server for [Matrix](https://matrix.org/), an open standard for decentralized persistent communication. ([Source Code](https://github.com/matrix-org/synapse)) `Apache-2.0` `Python`
 - [Syndie](https://syndie.de) - Syndie is a libre system for operating distributed forums. `CC0-1.0` `Java`
 - [TextBelt](https://github.com/typpo/textbelt) `⚠` - Outgoing SMS API that uses carrier-specific gateways to deliver your text messages for free, and without ads. `MIT` `Javascript`