Gajim

Gajim is an instant messaging client for the XMPP protocol which uses the GTK toolkit. The name Gajim is a recursive acronym for Gajim's a jabber instant messenger. Gajim runs on Linux, BSD, macOS, and Microsoft Windows. Released under the GPL-3.0-only license, Gajim is free software. A 2009 round-up of similar software on Tom's Hardware found version 0.12.1 "the lightest and fastest jabber IM client".

WWW Official Site

Features

Gajim aims to be an easy to use and fully-featured XMPP client. Gajim uses GTK (PyGObject) as GUI library, which makes it cross-platform compatible. Some of its features:

Group chat support
Emojis, Avatars, File transfer
Systray icon, Spell checking
TLS, OpenPGP and end-to-end encryption support
Transport Registration support
Service Discovery including Nodes
Wikipedia, dictionary and search engine lookup
Multiple accounts support
D-Bus Capabilities
XML Console
Jingle voice and video support
OMEMO encryption
HTTP file upload
Read markers
Hats

Gajim is available in Basque, Bulgarian, Chinese, Croatian, Czech, English, Esperanto, French, German, Italian, Norwegian, Polish, Russian, Spanish, Slovak, Swedish, Ukrainian and others.

Third-party plugins

Gajim supports various third-party plugins.