Gajim is a free chat client for the XMPP (Jabber) protocol that runs on Windows, macOS, Linux and BSD. It is written in Python with GTK. Users can pick any XMPP provider and sync chats across their devices. Features include one-to-one and group chats, reactions and replies, voice messages, file transfer via HTTP file upload, multiple accounts, service discovery and an XML console. Messages can be encrypted end to end with OMEMO and OpenPGP, and with OTR through a plugin. Voice and video calls via Jingle were removed in version 2.0.0.
Gajim is released under the GPL-3.0 and developed by volunteers; its first release dates from 2004. It is a client, not a hosted service: accounts and messages live with whichever XMPP provider the user selects, which may be a provider in the EU or a server run by the organisation itself. Sovereignty therefore depends on the chosen server and the encryption settings. The open protocol and open source code allow inspection and independence from a single supplier.