Bicycle chains are pretty complicated, but steam powered devices (mills, saws, etc) were using flat leather belts for decades, and rope drive existed as well. M

Bicycle chains are pretty complicated, but steam powered devices (mills, saws, etc) were using flat leather belts for decades, and rope drive existed as well. Many modern bicycles come with belt drives. Also periodically people produce shaft drive bicycles which require a bit more machining, but have few moving parts and are quite reliable.