Daniel wrote an article earlier this month detailing 5th Cell's Hybrid, a multiplayer shooter which is still surprising for me even after a year since its announcement considering the developer's creative success with Scribblenauts.
5th Cell promised that beta sign-ups would be ready soon and, well, they're available now! You must have an Xbox 360 and Xbox Live Gold Account to sign up for the closed beta, and you can earn an exclusive gold-plated beta helmet for your efforts.