Want to fight off swarms of the undead, but your computer can't run Left 4 Dead? Try Left 4K Dead: the concept of the original game distilled into a 2D, top-down shooter less than four kilobytes in size. Then, get a new computer.
Sure, it's no Mirror's Edge 2D, but Mirror's Edge 2D wasn't smaller than four kilobytes, either. L4KD is the brainchild of Markus Persson (his entry for the 2009 Java 4K Competition). Even if it resembles the real deal in much the same way that a brick resembles a house, squeezing the core concepts of a full game down to something you could have easily fit on a floppy disk back in days of yore is certainly worth a pat on the back or five.
The premise is simpler than that of the original (itself pretty damn straightforward) - you are controlling a character in a 2D, top-down world. There are lots of zombies. Kill the zombies before they kill you. Advance through levels. Go you! Sure, it's not particularly complex (though the flashlight effects are actually pretty cool, especially given the file size) but it's a fun time-killer.
If, to quote the Bard, "brevity is the soul of wit," then condensing a full-budget blockbuster title like Left 4 Dead (or Mirror's Edge) into a simple browser game and still retaining the essence of the original must be the soul of game design. Or something like that, anyway.