Saijo George has a post on 1800pocketpc.com telling of a new NES emulator for WP7. As previously reported here, Matt Bettcher’s open source NES emulator has been blocked from the WP7 Marketplace due to potential copyright issues, though he continues to campaign for its release. Tuska on xda-developers.com, without attempting to go through the Marketplace, has released a .xap for his own alternative emulator, which requires a developer-unlocked device to use.
You can read more, with download links, at 1800pocketpc.com here or on the original xda-developers threat here. Be advised that the app is currently limited to portrait mode and is reported to be slow and buggy, though Tuska is continuing to update and optimise it.