I discovered Pidgin in 2010. We could use chat system via a plug-in, and out school were using their "own" protocol for an internal chat system, AKA NetSoul. You either had the choice of the CLI NetSoul client, a GTK one not-so-great, or a plug-in into that awesome thing that is Pidgin.

Nowadays I use it For Lync, the Business version of Skype.