Litecoin is a peer-to-peer Internet currency that enables instant payments to anyone in the world. It is based on the Bitcoin protocol but differs from Bitcoin in that it can be efficiently mined with consumer-grade hardware. Litecoin provides faster transaction confirmations (2.5 minutes on average) and uses a memory-hard, scrypt-based mining proof-of-work algorithm to target the regular computers with GPUs most people already have. The Litecoin network is scheduled to produce 84 million currency units.
From Litecoin.info, where you can get more information on using, acquiring and mining LiteCoin.
The official website, Litecoin.org has additional information and links to Litecoin clients/wallets.