Vroom! is a game for Windows and iOS about running over zombies in a big blue truck. It's a spinoff of the Half-Life 2 mod Shotgun Sunrise, which was a community project on the G&T forum back in 2008-2009, and is made by some of the same dudes. We made it in around four months, originally for iOS, and recently we released a PC version, which has better graphics and more zombies.
You have a time limit, and you add seconds to the clock by going through checkpoints and smashing as many zombies as possible. The goal is to keep the round going as long as you can. You can add boost to your Vroomometer by hitting zombies. Correct procedure is to pretty much be boosting super fast 100% of the time.