2300AD is a roleplaying game set in the 24th century. Man has travelled to the stars and created colonies there. Aliens have been discovered - some friendly, some hostile and some just plain weird. The Game is what could be considered hard SF and is wide open in its scope.
Players can be colonists, military, scientists or thugs - all with equal ease.
Though it has never had a huge following it still stands out as one of the best SF games ever produced.