What is OpenZDK?
OpenZDK is the Open Zune Development Kit. Not enough detail for you? OpenZDK allows you to make and play games and applications for the Zune of much higher quality than was possible before. OpenZDK eliminates the limitations of XNA and makes it possible for independent developers to build programs on par with Audiosurf Tilt, PGR: Ferrari Edition, MSN Money, and other first-party titles from Microsoft.
How do I install native Zune applications?
If you have ever installed an XNA game, it can be as easy as running the application's installer! See the getting started guide for end users for details.
Why would I want to use native Zune applications?
Native Zune applications allow developers to create applications of much higher quality and capability. Native Zune applications run several times faster and can work in 3D, access the internet, run in the background, and do many things we haven't even thought of yet.
Why not just use XNA?
While XNA makes simple game development much more accessible to the masses, anyone who attempts to use it to build advanced games and applications will quickly discover that it is inherently unsuited for anything that needs to go beyond the essentials. Quite a few of the applications released by Microsoft could not be built purely using XNA without extensions that are withheld from third-party developers.
Will this damage my Zune?
No. As things stand right now, all changes done by OpenZDK and OpenZDK applications can be reversed. However, with great power comes great responsibility - due to the extended set of capabilities afforded to applications through OpenZDK, you must not install such applications with the same lack of concern that you might have with traditional XNA applications. As a result, you should only install applications from individuals you trust and those that have been confirmed by other users as non-malicious. Even in the highly unlikely event that you do install a malicious application, resetting your Zune should wipe the slate clean in nearly all cases.
Will this void my warranty?
No. Installing OpenZDK-enabled applications on your Zune is akin to installing Firefox on your PC. It is highly unlikely that Microsoft currently checks your Zune's contents upon receiving your device for repair. In addition, there have been no cases of OpenZDK apps causing any irreversible damage to a Zune device. Microsoft has no legitimate reason to deny a warranty claim due to the existence of an OpenZDK application or game. However, in any case, it is highly recommended to fully reset your Zune if possible before sending it in for warranty repair - this will eliminate any trace of OpenZDK applications that could pose potential issues.