This is Converse.js (version 10.1.6) in Tauri connecting to any XMPP server through xmpp-proxy.
It's the first known client to support QUIC.
To build install Tauri cargo install --locked tauri-cli, then run cargo tauri build.
If you want to download binaries head over to Releases.
MPLv2 - Converse.js files under dist/ excluding 3rdparty/
GNU/GPLv3 - dist/3rdparty/libsignal-protocol.min.js
GNU/AGPLv3 - Rust files under src-tauri/ - Check LICENSE.md for details