The rules were either 3e or 3.5 with the following changes:
- Humans were not allowed to multi-class, except to join a single prestige class. (This effectively locked humans out of certain prestige classes like Eldritch Knight and Mystic Theurge, which exist only to aid and abet multiclassing.)
- Human PCs could pick any feat out of the book with no regard to prerequisites. So, for example, someone could just take Great Cleave without taking Power Attack and Cleave before it. Nor did they need a Str 13 or Base Attack +4. Nonhumans still had to follow the usual requirements.
- Players of human characters were also encouraged to use feat slots on anything they wanted to be able to do that wasn't covered by the Feat rules in the Players Handbook. I.e. instead of buying other products to find weird ass feats, just work with the DM to write your own.
That's all I remember, except for the fact that buddy Chris liked the feat rules for humans. To the best of my knowledge he's never played any edition past AD&D2, but he's definitely the kind of player who doesn't want to read the rulebook in detail to plan out a character.