What are the differences between Bitcoin and Litecoin? What are the differences between the Bitcoin and Litecoin algorithms and protocol?
Litecoin is exactly like Bitcoin, but:


The hashing algorithm is CPU-friendly, meaning that having powerful GPU doesn't let you mine fast.
The difficulty of the blocks is set so they would be mined about every 2,5 minutes, instead of 10.


Other differences are cosmetic, like aiming to generate more Litecoins than there will be Bitcoins, using different port, etc.