With the understanding that ask a dozen people what "OSR" means and you'll get a dozen answers. Can you name me some of these OSR games?
In this instance, I am using "OSR" to indicate a rules set based on OD&D or B/X D&D.
There will probably be some overlap with Aramis's list.
Primarily OD&D:
Bandits & Battlecruisers
Colonial Troopers
Humanspace Empires (Tekumel/Empire of the Petal Throne clone)
Warriors of the Red Planet (Think John Carter of Mars)
White Star (Based on Swords & Wizardry)
X-Plorers
Primarily B/X D&D:
Hulks & Horrors
Machinations of the Space Princess (Based on Lamentations of the Flame Princess)
Mutant Future (Think Gamma World. Based on Labyrinth Lord)
Shards of Tomorrow
Space Madness
Star Wars Galactic Adventures
Starships & Spacemen (Based on Labyrinth Lord)
Tales of the Space Princess
Stars Without Number seems to use several systems and has a heavy Traveller influence.
There are probably a couple more that I've missed, not counting "Old School" games which are not based on D&D.