https://github.com/inetic/club
It is a library for decentralized networking designed (not only) for computer games with the main goal to avoid paying for game servers.
People asked me whether it can be used for real time multiplayer games and since there wasn't a game using it already I hesitated to give a yes/no answer.
Since then I started to work on this little game. It is a space shooter game with ugly graphics with the main goal to showcase Club.
https://play.google.com/store/apps/details?id=com.sicoop
Given that Club is still in its alpha stage, I think the result is good. When players connect using WiFi I was able to play with 4 players simultaneously. I had problems when I connected through my mobile carries because my mobile internet is slow and Club currently lacks a congestion control mechanism.