I started developing SnowballZ back in 2006. Since then it has undergone three major re-writes. In the last one I think it is finally ready for others to start contributing. Not just content but code also.
I have put effort into making the code clean and understandable; easy to get started working on. If you are interested in helping the development see how you can get started.
The last released version of snowballz was 0.9.5.1. The source is a mess and it is not recommended that you look at it. If you are just wanting to play it grab the binaries from Arctic Paint. At this point that is the only playable state of the game.