James Hargrove has recently a very nice rules light RPG called ZIP! The entire set of generic rules is 3 pages of fairly large print (with room for some art) -- four pages with the OGL. Yes, the entire game is open game content.
According to James, these rules are based on the set of rules he has been using for play-by-email games for the last ten years or so. The rules are modern but have a firm basis in old school style play. Simple rules with a lot left up to the GM. Success rolls are 3d6 with bonuses and penalties assigned by the GM based on the situation and the character's archetype, attributes and weaknesses. The game is designed for a narrative style of play. No minis or battlemats are required.
You can download a copy here: ZIP! Core Rules PDF
James has also released a setting supplement for ZIP!: Hawkmoor. James describes Hawkmoor as follows in his ZIP! Blog:
Hawkmoor is a fantasy supplement for ZIP in the vein of the original Dungeons & Dragons supplements Greyhawk and Blackmoor, though it's not just another retread with the serial numbers filed off. Now, I'm all for old-school settings, but back when I was running Hawkmoor everybody seemed to be reinventing the same old wheel and simply calling it something different. I didn't really want or need multiple clones of settings that I already owned, so I designed Hawkmoor with a few specific goals in mind.While it doesn't set out to be OD&D, ZIP! with the Hawkmoor supplement makes it very easy to run the types of campaign's 0D&D players like with a streamlined set of rules that most players will think of as "modern rules." It would be easy to modify Hawkmoor to be closer to OD&D in feel if one wanted to. The Hawkmoor supplement is 10 pages (11 with the OGL) with large print and artwork. Like the core rules, the Hawkmoor text is entirely open game content.
First, Hawkmoor is an implied setting, just like the original Greyhawk and Blackmoor. That is, the setting is conveyed via rules (in this case, racial archetypes, occupational archetypes, a magic system, monsters, and so forth). Second, I wanted to take common conventions of classic D&D and turn them on their heads — for example, Hawkmoor has magic, but it's not 'fire and forget magic; Hawkmoor has werewolves, but they're in thrall to evil sorcerers; Hawkmoor has priests, but they don't cast spells (although they do heal); and so on.
So, Hawkmoor is an homage to original D&D, not a simple copy and paste job. It's not a retro-clone.
You can download a copy here: ZIP! Supplement 1: Hawkmoor
While I haven't had a chance to run a session of ZIP!, I really like what I've read. ZIP! looks like it would be another way to introduce "new school" players to the "old school" style of play using a set of rules that probably will not seem "old school" to them. Better yet, it looks like a fun game to play regardless of your "RPG School" affiliation. Give ZIP! and its Hawkmoor supplement a look.