Openfire - Openfire (formerly Wildfire) is a cross-platform instant messaging (IM) and groupchat server.
Ripcord - A desktop chat client for Discord and Slack
Prosody - Prosody is a modern flexible communications server for Jabber/XMPP written in Lua.
Slack - A messaging app for teams who see through the Earth!
Matrix.org - Matrix is an open standard for decentralized persistent communication over IP.
Ziggs - Smoothly Share Content Between Devices!