I mentioned this in the "Free SF RPGs" thread, but I think Exiles really deserves some recognition, so I''ll re-post the info here:
From the people who brought us (a simple universal game) and , (about playing angels in the struggle of good and evil) there is the SF RPG . After a new "dinosaur killer" sized asteroid strikes Earth, the only survivors are those living in underwater habitats.
Its mostly hard SF, though there are rules for psychics. Super-cavitation submarines are in fact a current area of research. (note the torpedo!) The setting is quite detailed, and I find the system powering the game quite innovative - each roll can tell you three things. It begins as a basic [Attribute+skill+d100], but its the presence of 1 or not (ie over 100) that determines success, the 10s digit is the degree, and in combat, the ones place is where you hit the target. Not the usual roll under percentile. (The game is from circa 2005, so I belive it predates the "One Roll Engine" also designed to tell multiple-points from one roll)
For a free game, its a very professional lay-out, and has quite a few pieces of artwork. Placyers trapped inside high-tech cities is a far cry from the usual post-apocalyptic milleu of being stuck outside the few bastions of humanity.