Adium
Software
Adium is a free and open-source instant messaging client for macOS that supports multiple IM networks, including XMPP, IRC and more. In the past, it has also supported AIM, ICQ, Windows Live Messenger and Yahoo! Messenger. Wikipedia
Initial release: September 28, 2001; (22 years ago)
Preview release: 1.5.11hgr5899 (January 15, 2015; 9 years ago)
Stable release: 1.5.10.4 (April 27, 2017; 7 years ago)