Indentured servitude: An arrangement where individuals would work under a contract for a certain period in exchange for something (usually passage to another country).
Sharecropping: A system common after the American Civil War where farmers (often former slaves) would work on someone else's land and give them a share of their crops as payment.
Serfdom: A medieval labor system where peasants were bound to work on their lord's land in return for protection and the right to stay on the land.