Steam Instant-Messenger was a system I used a lot at the time, but it didn’t support Windows Phone.

Using some reverse-engineering of the protocol Valve used for the Android / iOS versions, my application was able to logon to the Steam servers (including 2-factor authentation) and send/receive messages from users on your friends list.

Mock-up of application. Above is a mock-up of the application, created whilst designing the look and feel of the application.

Login screen

Message page

I found the application useful at the time. Unfortunately the app didn’t have background notifications, I believe the API didn’t support that at the time. I was close to packaging it up for publishing, however users had to type their Steam credentials into a third-party application. For this reason I decided not to persue publishing.