Some time ago a game called Polarium was released for the Nintendo DS (and also the Gameboy Advance), it's a game where you have to draw a line to flip over tiles. And now someone has made a homage (okay, so it's a blatant rip-off) of Polarium called Backflip which you can play online. And you can make your own levels which you and others can play.

The instructions show you exactly how to play the game, and you can sort puzzles by rated difficulty and other things.