Bitcoin is the original cryptocurrency for payments processing. It's known for network congestion and high transaction fees. Many young altcoins are attempting to address these issues.
Ethereum is the original cryptocurrency for smart contracts. The CryptoKitties game has caused network congestion and high transaction fees. Some 2nd Layer tokens centralize/localize off-chain player activities, allowing specific transactions types to occur on Ethereum.
GridCoin is the original cryptocurrency for P2P computing, specifically designed for scientific communities to increase their computational abilities through citizen-scientists who share their personal hardware.