Focus by jesse venbrux is a really great insanely fast-paced platformer, saying any more would spoil it. There are challenges for time trial and low-death runs for those who really want a challenge.
I'm running the game on a computer which has no support whatsoever for vsync, which needless to say is slightly annoying. Using -30fps as a run command fixed the timing for every level except for 7-19X, which was made essentially impossible (the doors close behind you too fast, or they originally open too slowly, I'm not sure which, but you can't get to the end fast enough). Googling only confirmed I wasn't the only person to experience this problem, but yielded no solution.
Thought I'd post this here ;)
ps I beat the level by copying my saves onto a friend's computer and doing it there, which finally got me the achievement for cotton alley dark world :D