There's nothing like insane constraints to bring out the best in people! Take the recent js13kGames competition, where developers were given a month to whip up a browser game no bigger than 13KB. Here are some of the cooler ones... and they will surprise you.
The rules are simple: write a game that runs in a browser, is no more than 13KB compressed, and has no external dependencies, be they images or code libraries. You read that right: 13,312 bytes for code, graphics and everything else the game needs.
Lee Reilly, a developer at GitHub and one of the competition's judges, put together a list of 13 favourites, including the isometric shooter UNDERRUN, side-scrolling beat 'em up The Matri13k and the planetary tower defence game, Exo.
The great thing is, you don't need anything to play these games. Well, except for a browser of course. Even better, if you want to learn how any were made, uncompressed source code is available, too (here's UNDERRUN, for example).
If you'd like to check out all the entries, hit up the js13kGames website. I'll warn you now: there's a lot.