Windows Live Messenger is an instant messaging program from Microsoft.  Formerly MSN Messenger Service.

Native alternatives for non-windows platforms
- Gaim (works with Yahoo!, MSN, ICQ and many others)

- Kopete (supports advanced MSN features. Part of KDE's PIM package (kdepim))

- aMSN (supports webcam, nudge, inkdraw and other advanced MSN features)

Collection of Windows Live programs with a unified installer. Includes Windows Live Messenger, Mail, Photo Gallery etc

Note: This is for the installer only, please submit results for the individual apps to their appdb entries (see below).