Microsoft Notification Protocol (MSNP, also known as the Mobile Status Notification Protocol) is an instant messaging protocol developed by Microsoft for use by the Microsoft Messenger service and the instant messaging clients that connect to it, such as Skype since 2014, and the earlier Windows Live Messenger, MSN Messenger, Windows Messenger, and Microsoft Messenger for Mac. Third-party clients such as Pidgin and Trillian can also communicate using the protocol. MSNP was first used in a publicly available product with the first release of MSN Messenger in 1999.