A real game based on the Royal Wedding would be boring as all hell. You'd be managing sliders based on protocol and a receding hairline. A game based on the Royal Wedding when it's under attack by zombies, now that's more like it.
Class 3 Outbreak is a simple web game that lets people model the effect a horde of zombies would have on the civilian population of a real-world location (it uses Google Maps data). To commemorate the upcoming Royal nuptials, the game has added a "Wills & Kate" map, complete with wedding march and Westminster Abbey.
While you can't control the humans or zombies directly, you can "manage" the game via a series of settings, so if you'd save the day or see the future King of England consumed by the undead, it's got you covered either way.
Royal Wedding [Class 3 Outbreak, via Tecca, thanks Mike!]