Openfire - Openfire (formerly Wildfire) is a cross-platform instant messaging (IM) and groupchat server.
HexChat - HexChat is a fork of XChat with bug fixes and new features.
Prosody - Prosody is a modern flexible communications server for Jabber/XMPP written in Lua.
mIRC - mIRC: Internet Relay Chat client
Matrix.org - Matrix is an open standard for decentralized persistent communication over IP.
irssi - Irssi is a terminal based IRC client for UNIX systems.