Bitcoin faucet apps are mechanisms to dispense small amounts of bitcoin for testing or promotional purposes to interested parties. The concept was originated by Gavin Andresen, who created and administrated a faucet project in the early days of Bitcoin.
One major weakness of the concept is that there is no ready way to prevent a person from masquerading as another person to receive additional Bitcoin. Another weakness is the Bitcoin network's poor support for transfers of very small amounts.
Given these weaknesses, the only reliable faucets tend to be those for test networks like the Bitcoin testnet, where the distributed tokens are designed to be valueless.