Tons of answers in the comment section already, I personally know of Freebitco, which to me, is more of a time waster than earning free bitcoin.
When bitcoin was cheaper in price, I used to use freebitco faucet to earn some really significant amount of satoshies, but I tried the platform of recent, and discovered that the amount of satoshi that can be earned per hours has gotten to as low as 0.00000001 which to me, is a waste of time, but still worth giving a try if really you can't afford to buy $10 worth of bitcoin to gamble with.