Trillian is a proprietary multiprotocol instant messaging application.

Instantbird is a cross-platform instant messaging client based on Mozillas XULRunner and the open source library libpurple used in Pidgin.

AIM is a instat messenger application.

Franz is a free messaging app /former emperor of Austria, that combines chat & messaging services into one application.

Smuxi is a cross-platform IRC client for the GNOME desktop inspired by Irssi.