This is so big game where you need hit and make goal. Simple gameplay and hard logic. Game project consist of three parts:
Self game. You can change here what you want. Any image and sound.
Multiplayer module. This is so big part. We using scirra signaling server and this is peer-to-peer connection. Note: I not garant that this is will works in all devices. You can test it easy – open one player in one browser, second in another. This is need, because player ID saving in local storage. If you wont play with self – better use different browsers. Also, please note that sometimes routers can just block connections, so better if you will play dirrectly.
Server part. Here is we collect and saving players data. Columns in database is: id, nickname, rating, hits, targetHits, wins, games, playerID and authKEY. Nothing personal. Player just register in automode in the game. Then he can play with another players. Also you can transfer player progress. For this just copy player ID and put it into another device.