When I was in high school our school sucked, because they only had Macs. That's right, no cool stuff like quake inbetween periods. But there was one game for the poor old Mac OS that even our outdated school computers could run, NS Shaft. This is a 21st century remake of that truly amazing game.
The controls are simple, left and right arrow keys. Avoid falling off the bottom of the screen and don't get crushed by the spikes in the collapsing ceiling. The longer you can survive, the higher your score.
If you step on a red platform you lose some health, but you can regain it by stepping on non lethal platforms. There are also some conveyer belts and spring boards to keep you on your toes.