My favorite recent one was a group that wanted to go with Bronze Age(ish) tech level, so we arrived at the notion that the world was "young." There were no fighters, because no societies specialized enough to have professional soldiery who would train up to that level. No martial weapons, no heavy armor. Only classes were barbarian, druid, ranger, rogue (no AT), and WM sorcerer.
Then we wanted it to be in the Himalayas, so the only races were two human clans (one, statistically, half-orcs), goliaths, and svirfneblin.