Coins

Coins are used in most zynga games. You do not need to pay for them unlike cash.

Games That Use Coins
Cafe World: gained by serving costumers.

FrontierVille: gained by feeding animals, harvesting, and bonuses.

Treasure Isle: gained by finding them or completing islands and collections.

YoVille: gained by working.

FarmVille: gained by harvesting.

PetVille: ?