Dino is a modern open-source chat client for the desktop.
Ferdi
Ferdi is a messaging browser that allows you to combine your favorite messaging services into one application.
Polari
IRC client which enables you to chat with people around world through large chatrooms or via private messaging.
Jami
Share, freely and privately. Decentralized messenger with VOIP.
Fractal
Fractal is a Matrix messaging app for GNOME written in Rust. Its interface is optimized for collaboration in large groups, such as free software projects.