Windows Live Messenger is Microsoft's instant-messaging service. Once called MSN Messenger, Windows Live Messenger is a chat client that also works with Yahoo's IM protocol. Users can text and video chat, as well as make calls and send SMS text messages to telephones. It also has a shared file storage system that lets users swap and store files.
Windows Live Messenger is available on several platforms including mobile phones. It's even been integrated into Microsoft's gaming console, the Xbox 360. All versions require users to sign up with Microsoft's Live ID identification system.