Halo: Spartan Assault has today been confirmed by Microsoft for Windows 8 Phone, Windows 8 PC and Windows 8 tablet game.
Apparently it'll feature in-app purchases and is around 25 missions long. It's also not your usual Halo game, since it's a top-down shooter.
The story is said to bridge the gap between Halo 3 and Halo 4, while Halo 4 players will be able to earn XP, achievements and medals. Stat-tracking will also be incorporated via Halo Waypoint and multi-platform play will allow progress to be tracked across all of your Windows 8 devices (That's if you're one of those illusive people with a Windows phone or table of course).
Anyway, here's a trailer.