Is there a tutorial anywhere on how to create a new game definition?
there's a wiki page at wiki.octgn.net which has a lot of resources for game development. There's a game editor that is currently being worked on which will be helpful for new game developers who aren't comfortable with XML and Python (the languages that games are written in). But until it's finished, you'll have to dive into the XML code. You can also take apart an existing game definition and use its structure to help get a new game built.