Gamerservices is a system much like Steam. It allows gamers to download games, get achievements, get leaderboard positions, etc. It also allows developers to post their game on the site and the GS client for free. Via the API, the achievements and leaderboards are simple to approach. There is an easy to use library for .Net that allows you to communicate with the platform with just a few lines of code.
The development on GS has not continued for a long while though, as I’ve since moved on to other projects.