A universal instant messaging (IM) program
See https://pidgin.im/about/ for more information. Pidgin is an instant messaging program which lets you log in to accounts on multiple chat networks simultaneously. It runs on Windows, Linux, and other UNIX operating systems. Pidgin is compatible with the following chat networks out of the box: AIM, ICQ, Google Talk, Jabber/XMPP, MSN Messenger, Yahoo!, Bonjour, Gadu-Gadu, IRC, MXit, Novell GroupWise Messenger, Lotus Sametime, SILC, SIMPLE, MySpaceIM, and Zephyr. It is written in C and makes heavy use of GLib and GTK+. Finch is a command line instant messaging program. It also lets you log in to accounts on multiple chat network simultaneously, and it is compatible with the same chat networks as Pidgin. It is written in C and makes heavy use of GLib and ncurses.
Psi IM — Qt-based XMPP/Jabber client
Psi aims to be a feature-rich Jabber/XMPP client for novice and experienced Jabber users. There are builds available for MS Windows, GNU/Linux and macOS.
Psi+ Project — Development branch of Psi IM XMPP/Jabber client
Psi is a cross-platform powerful XMPP/Jabber client (Qt, C++) designed for the Jabber power users. Psi+ is a development branch of Psi IM XMPP/Jabber client. Project Purpose: collection, refinement and writing new patches for transfer them to Psi upstream developers.
A fork of pidgin which aims to provide minor features that have not been addressed by the pidgin development team (including manual textbox resizing). See funpidgin.sf.net for details.
XMPP PHP BOT (XPbot) - simple, extensible jabber bot
XPBot or rather Xmpp Php Bot is an extensible, modular and modern XMPP(Jabber) bot written entirely in PHP. XPBot utilizes all major PHP 5.4 and in feature we're gonna probably move our code base to 5.5 version to provide even better user (and developer!) experience. This bot is going to be 100% modular, so you can replace almost every part of the bot. It's of course free to use (even commercial!). Want to know more? Look at our homepage (Work in progress).
JGGAPi is java implementation of Gadu-Gadu protocol. Gadu-Gadu is a IM system very popular in Poland based on proprietary protocol. The implementation is based on specification of Gadu-Gadu protocol gathered during implementation of EKG application.
OpenSource Jabber blog system written in Perl.