Crayons. Crayons, crayons, crayons. Crayons!
In conclusion, crayons are great.
Also great is Crayon Physics Deluxe, which kindly Old Man Eurogamer let me spend an afternoon playing this week. You can read it by following this passage of tantalising text:
There's something sublimely magical about drawing something and having it come to life. It's like being Penny Crayon without the squawking horror of Su Pollard providing your voice. Combined with the childhood pleasure of the thick, comforting lines of a crayon, you've got a puzzle game that hurts your brain while making you feel warm and safe at the same time.
And play the free previous version here.