Carmageddon was released in 1997 and was one of the first games where the environment was completely open and you didn't have to stick to the track. It also had a great Fear Factory soundtrack and gave you points for running over pedestrians (or zombies)! It was one of my favorite games when it came out.

OpenC1 is an open-source remake of Carmageddon. It uses XNA for the graphics and Nvidia PhysX for the physics. It implements almost all features of the original game, including vehicles, tracks, vehicle damage, pedestrians, opponents, checkpoints, UI, breakable, bendable track objects, animations. It does not currently implement powerups or network play.

As of version 1.4, OpenC1 can auto-download the free Carmageddon demo content (artwork, models, etc) so you can experience OpenC1 without having to own the full original game.