I would recommend Fudge, in part because it moves away from numbers for stats and because it is sort of a build-your-own-system system, and part because it is free. Fate is based off the same mechanics.

As an oddball option, Warrior Cats RPG, because it is free, and because it is diceless. Honestly, there are better systems (including better diceless systems) out there, but not so easily accessable. At least see how it works out.

Finally, I will recommend being familiar with the Tri-Stat system. Not because it is particularly good, but just as another way to look at how to do a RPG.