Spellcraft & Swordplay by Jason Vey.
Now, just I get this out of the way first. Jason is a friend of mine and we worked on a lot of Unisystem games together. Also I worked on a supplement for S&S called Eldritch Witchery that is due out soon. That all being said I developed my opinion of this game long before EW ever was thought of.
When D&D was starting out it grew out of the rules in Chainmail. Using a d20 (twenty-sided die) was the "alternate" combat method that became the norm. But the original combat method involved 2d6 (two six-sided dice), S&S (among other changes) explores that further.
There are other changes such as saving throws are made against the appropriate ability (which is not to far off to how 3rd or 4th ed does it) and there are no skills, but ability rolls.
So in many respects it is a much simpler game than the other clones.
I have written a rather long review here for the core book:
I wrote that before I got the gig to write EW. In fact I got the book, read it, reviewed and then convinced Jason to let me write EW.
If you are new to this sort of game or want to check it out then PLEASE give this a shot. All you are two normal 6 sided dice, just like the ones in your Monopoly game to get started.
There is the core book, Spellcraft & Swordplay and a supplement, Monstrous Mayhem.
Both PDFs and print copies are on sale now. Plus if you buy the print copies you can get the PDFs for free.
I really can't say enough about this game. In fact here are my old posts about it.
Get it. You can thank me later.