I heard about this in F-Droid’s latest blog post.
It is based on the Bramble protocol and is compatible with Briar.
It removed mesh-networking features of Briar and added a couple new ones:
- voice messaging
- ML-KEM (post-quantum cryptography)
- disappearing messages
More technical details are shared on their blog.
Sources are on Github https://github.com/zerionproject/Zerion
You can connect to SimpleX over tor, and you can run SimpleX servers over a tor hidden services.