Going Off The Rails
I'm hooked on Rollacoasta. All you do is build a roller coaster that scores the most points. Sounds easy right? Not. The physics behind this game are amazing. I've even got a couple loops to work (though not all the riders appreciated it). What's even better is that it's Gamemaker so the code is available to review. I could see a physics or programming class spending time tearing this one apart. If the web version doesn't work, just download the executable and install on your computer.