Skein is a new family of cryptographic hash functions. Its design combines speed, security, simplicity, and a great deal of flexibility in a modular package that is easy to analyze.
Skein is fast. Skein-512 -- our primary proposal -- hashes data at 6.1 clock cycles per byte on a 64-bit CPU. This means that on a 3.1 GHz x64 Core 2 Duo CPU, Skein hashes data at 500 MBytes/second per core -- almost twice as fast as SHA-512 and three times faster than SHA-256. An optional hash-tree mode speeds up parallelizable implementations even more. Skein is fast for short messages, too; Skein-512 hashes short messages in about 1000 clock cycles.
Skein is secure. Its conservative design is based on the Threefish block cipher. Our current best attack on Threefish-512 is on 25 of 72 rounds, for a safety factor of 2.9. For comparison, at a similar stage in the standardization process, the AES encryption algorithm had an attack on 6 of 10 rounds, for a safety factor of only 1.7. Additionally, Skein has a number of provably secure properties, greatly increasing confidence in the algorithm.
Skein is simple. Using only three primitive operations, the Skein compression function can be easily understood and remembered. The rest of the algorithm is a straightforward iteration of this function." - Bruce Schneier
Read more: http://www.schneier.com/blog/archives/2008/10/the_skein_hash.html
Download the whitepaper: http://www.schneier.com/skein.pdf