Smuxi is an open-source, powerful, flexible, and user-friendly chat client created by Mirco Bauer and developed by other contributors. Inspired by the combination of screen and irssi, Smuxi has a detachable server (or like a "normal" client) that stays connected when you aren't, and can allow multiple Smuxi frontends (like the GNOME frontend, or STFL text-based frontend) to be connected and in sync. This is similar to screen+irssi or IRC bouncers, but more elegant and powerful.
Smuxi was created in 2004 when Mirco Bauer could not find a client quite like irssi running in a screen session. Although this was ideal for leaving connected, it didn't integrate with the desktop well. Smuxi was developed to fit this need, with irssi being a major influence into the way it behaves.
Smuxi is powered by C# and Mono. The libraries used include SmartIrc4net, Newtonsoft.Json, ServiceStack, Twitterizer, agsXMPP, STFL, GTK#, and many more.