Bitcoin: "Magical internet money" handed down to us from upon high by The Satoshi Nokomoto. The origional crytpocurrency.
Litecoin: Bitcoin with lower fees, more stable prices and faster transaction times.
Ethereum: "Turing-complete" (theoretically it could be used to solve any computation problem) platform for decentralized applications (ie Smart Contracts).
(TL;DR: Platform for ICO's)
Monero: Privacy coin, doesn't include amounts, origins or destinations for any transactions.
Ripple: Banks/Financial Institutions on the Blockchain via RippleNet to send money globally between them - basically an intermediary payment processor.
IOTA: Connecting the Internet of Things to the blockchain with no transaction fees (for data between IoT devices)
DASH: "Privately" mixes coins among centralized servers
...to be continued