You can contribute in several ways, helping code development, creating music and graphics, and translating the game content. All contributions have to be licensed under GNU GPL 2 or later, CC-by-SA or, for documentation, under GNU FDL (see License for more information). You should create a sourceforge.net account if you want to get write access to Git and join the team. Contact us.
New to the project? Find out Where to start as an artist