MSN compatible messenger application
A very nice MSN compatible messenger application, aMSN Messenger is a multiplatform MSN messenger clone. Works pretty much like its Windows based counterpart. Perfect for keeping in touch with those friends who have not yet seen the light. Works on linux
The PlanetaMessenger.org Libraries project is a set of open source instant messenger libraries used and maintained by PlanetaMessenger.org. You can find protocol implementation for MSN, ICQ, ComVC networks for use on standalone and server applications.