Monster Games, of Excite Truck fame, have been working on a top-secret Nintendo game for the last two years.
The Minnesota-based Monster Games produced Excite Truck for the Wii back in 2006, and according to a blog post on one of the game designers at Monster, the team are working on a highly-confidential game for Nintendo.
Right now, the 20 employees at Monster Games are working on a top-secret video game for Nintendo. They've worked on it for two years and are nearly finished. The process is so private the designers must darken their monitors when the bottled-water deliveryman enters the office.
With a lot keeping the project under wraps, it's likely to be a well-known Nintendo franchise. Their experience in producing racing titles and handling the Wii exceptionally well in Excite Truck suggests F-Zero, or a sequel to Excite Truck perhaps.
Thanks to NeoGAF.