Radical Entertainment has teamed up with Slice HD developer TwitchGames to offer ProtoSlice, a free app for iOS players looking forward to Prototype 2's release next year. Come to that, you can play it even if you're not sure what a Prototype 2 is: the only actual prerequisite is a fondness for reflex-gaming and a willingness to endure a fair amount of virtual finger-slicing.
Assuming you are into Prototype 2, you'll recognize the franchise's signature Arm Blades as the app's central obstacle. Maybe your mind's spinning with ideas for other apps based on the technology (James Heller: Fruit Ninja, Alex Mercer Has To Cut The Rope, etc). Radical's much wiser, though, to hold off letting you actually control the deadly blades until you fork out for the game in April 2012. You don't want just anyone running wild with those things.