What is Litecoin?
Litecoin is a cryptocurrency that uses an alternative, memory hard hashing algorithm called scrypt that was devised by mathematics' prodigy Colin Percival. The algorithm utilizes SHA256 and a stream function called salsa20 to force devices that mine it to either use a lot of memory or use dramatically more ALU cycles to perform a hash.  With the parameters used in Litecoin's implementation of scrypt (N = 1024; p = 1; r = 1), each thread uses approximately 64-128 KB depending on the settings for lookup_gap and thread_concurrency in the mining program when mining with a GPU.  Because GPUs have such fast memory (bandwidth in the hundreds of GB/s) and roughly 128-512 KB of RAM per stream processor, they are ideal for mining Litecoin.  This requirement for fast memory in order to mine quickly results in Litecoin being FPGA and ASIC resistant; although ASICs may one day come out for Litecoin, they are not expected to garner the same performance increases as for Bitcoin (two orders of magnitude more efficient).