Chalky is a stand up guy, or at least he tries very hard to be.
Chalky is a simplistic stick figure whose posture and behavior result from the mechanical constraints that define him. He consists of a set of 8 masses connected to one another through a series of damped springs with various coefficients. Gravity and instantaneous acceleration are estimated from your iPhone's X and Y accelerometers and transferred onto Chalky's virtual world.
Friction was further added to the edges of his frame along with some rudimentary stepping heuristics to give him a fighting chance to maintain his balance as you rotate your phone around or take him on the bus with you. You can also grab, stretch and throw him with your multi-touch screen if you feel he's not getting enough abuse.
Chalky also thinks he can dance and he'll start busting his moves if he detects music though your phone's microphone... so crank up the tunes!
Chalky is not artificially intelligent and none of his gestures are choreographed.
He illustrates the fact that humble perceptual measurements and simple constraints set in a physically meaningful environment can lead to interesting and sometime unexpected behavior.