What do you get when you cross prehistoric man with a group of combative ants and drop them in a few procedurally generated (and possibly space-themed) areas? I have no clue, but this edition of Weekend Download will probably be the closest thing to an answer you'll ever find.
Overgod (Windows/Mac/Linux, ~1MB, free) - A smart little shooter where you control a ship armed with a tiny gun facing handfuls of big enemies. Think classic Asteroids, only now the chunks of rock fire back. Choose from a selection of spacecrafts, each with a different ability, then fly around shooting everything that moves. Nab power-ups to stay in the game, and play it defensive for a better chance at surviving. Simple, but satisfying!
Ancient Ants Adventure (Windows, 14MB, free) - An isometric shooter with strategy/tactical elements and upgradeable weapons. You are the commander of battle ants on a quest to rescue soldiers. Battle bugs using a variety of weapons, gather gold to upgrade and unlock new tools to unleash havoc on the baddies. For the record, this game is far more fun than it should be allowed to be.
Caveman Craig (Windows, 7.5MB, free) - Lead your tribe of caveman as they survive the harsh prehistoric land filled with dinosaurs, dinosaurs, and more dinosaurs. Train cavemen as gatherers, hunters, and preparers, then teach them their skills to turn them loose for the good of the tribe. A great blend of action adventure gaming and a lite 2D simulation.
Space Game: Mujakwi (Windows, <1MB, free) - Imagine if you crossed old-school Metroid with a procedurally-generated shooter. Next, download Mujakwi and stop imagining, because that's exactly what it is. Explore the surface of a randomly generated planet in search of loot while taking out enemies along the way. Part of the TIGSource Procedural Generation competition.
Laser Bunny - Adventures in the Alien Death Mines! (Windows, 4MB, free) - Give a rabbit a laser and drop him in a series of randomly generated mazes and what will he do? Probably run around shooting alien-like creatures in a sort of Pac Man-type arcade shooter. Keep moving upwards to avoid the looming water, and grab power-ups to help you survive. Another entry in the TIGSource Procedural Generation competition.