So, given all the loving that the OSR community has for rules lite -or as I like to imagine them, concise rules, I'm surprised that I haven't seen mention of this nifty rules set: Dead Simple
It does an excellent job of presenting what you need for a core RPG in one page, and has several additional one page settings ( from SciFi thru steampunk, historical, asian (yeah, NINJAS !), and lost of setting additions for bog-standards fantasy (you know, "orcs, elves and halflings, oh my !"), a town an adventure, city rules, all nicely presented in single page format.
Seriously, check it out. NOW.