Post I.T. Shooter is small indie game by Kloonigames (run by Petri Purho, a computer science student in Finland, who each month creates a new indy game in seven days).
Unique aesthetics combined with a nice soundtrack, and randomly generated invaders!
The invader generator was inspired by Jared Tarbell’s Invader Fractal algorithm. Be sure to also check out Dave Bollinger’s Pixel Robots – also inspired by Tarbell’s work.
Crayon Physics allows you to draw objects using the mouse and let them interact with each other (by rigid body physics).
As of now Crayon Physics can be tested as a downloadable prototype, but a more complex version is under development.
Update: Marker World is a similar themed game, strongly inspired by Crayon Physics.
Experimental Gameplay started out as a student project at Carnegie Mellon University in 2005.
Given three basic rules (“Each game must be made in less than seven days / by only one person / be based around a central theme (e.g. gravity or swarms)”) some very interesting projects were created. Since then the website has opened up, and everyone is allowed to post their experimental games.
The experiences gained from the project are summed up in: How to Prototype a Game in Under 7 Days (Gamasutra Feature).
. Actually not a game, but beautiful none-the-less.