Celestial Mechanica is a quietly impressive platform adventure (a.k.a. "metroidvania") game along the lines of Knytt Stories and the Robot Wants series of games. Created by Roger Hicks (author of rComplex) and Paul Veer (animator of Super Crate Box), it's the sort of game that sits quietly off to the side, never begging you to play it, but once you do, you'll be hooked 'til the end.