Urban Terror is a free online First Person Shooter game on which I am the Lead Developer.
The team needed an auto-updater in order to be able to update the game really quickly for all the players and all the servers.
On the website side there is an API written in PHP which is called by the Updater to fetch the information needed to update.
The Updater is written in C++ using Qt. You can find its source code on my Github account.