Wikipedia
AMSN
aMSN is a free Windows Live Messenger clone. aMSN attempts to emulate the look and feel of Windows Live Messenger, and supports many of its features. It has been downloaded approximately 40 million times as of January 2011, making it the 21st most downloaded project on SourceForge.
aMSN is available for any system that supports Tcl/Tk 8.5 or higher, including Microsoft Windows, Macintosh and any UNIX/Linux variant, including Maemo ( Nokia's internet tablets) and OpenSolaris. A portable version for Windows is available by PortableApps.