Make a game on Nonoba have two authors. This is more needed now that you've added a payment system. It would mean the revenue from games could be split to a custom percentage between the contributors and so could the dev xp. You could then give options for version control aswell.
For example when making a game you could click 'Add Secondary Author' and a new row appears where you can type the name, the revenue split they receive and permissions for them to add/alter achievements or the game description and versions.