A toolkit called “OpenZDK” can bypass Microsoft’s limitations on developing programs for the Zune. The kit allow developers to make new games, port old ones, create emulators and even have a rogue app store on the device. It will work on the original Zune and Zune HD. OpenZDK could let people make applications on par with Microsoft-published games such as PGR: Ferrari Edition and Audiosurf Tilt. It could also spark a healthy homebrew community that would offer programs that are much better than what is available on the Zune now. The toolkit could allow programmers to get around the limitations Microsoft has placed. The OpenZDK crew met on ZuneBoards, a popular online Zune development community, where they go by usernames Netrix (aka Anderson), Nurta and itsnotabigtruck. It took them a few months to work around Microsoft’s protections, Anderson said, and they have been testing it for the last two weeks. But since OpenZDK has just launched, there are no apps or games based on it available yet. Getting started is easy enough, though, by following the steps.
More info: OpenZDK wiki