Just type RISUS RPG into your browser its a 100% free system the core rules around 15 pages. Its nicknamed the ANYTHING RPG and is as simple as it gets. Example each player uses CLICHES' roughly a job or character class for example if you took THIEF in a fantasy game it might be Burgler [Sneak Around, Break into Places with Lots of Funny Tools, Fight with Light Weapons, Lucky].
So you would have Cliche's that fit a really good action oriented spy- military ones, law enforcement, athletics, femme fatale, martial arts, communications, sciences or others. I use these rules because they are free, easy, cover lots of possibilities and work great for on-line games. Or convention pick-up games.