Facebook is the biggest online social network out there, and has long had an application available for BlackBerry where users could update their status, upload pictures, browse their news feed, and send messages. Facebook for BlackBerry integrates deeply with the device’s built-in notification and contact system. Facebook in and of itself is a popular application platform that, among other things, provides APIs for developers to use Facebook as a sign-up mechanism. On BlackBerry OS, there is also a Facebook Messenger app dedicated exclusively to chat functions.