P2Pool is a decentralized mining pool that works by creating a P2P network of miner nodes. These nodes work on a chain of shares similar to Bitcoin's blockchain. Each node works on a block that includes payouts to the previous shares' owners and the node itself. The share chain makes P2Pool 100% trust-less, miners are paid directly from the coinbase transaction when a block is found. There is no central point of failure, making it DoS resistant.
Resources:
Forrest V, P2Pool creators, homepage: http://p2pool.in/
P2Pool GitHub: https://github.com/p2pool/p2pool
P2Pool stats page: http://minefast.coincadence.com
P2Pool information: http://p2pool.org
Litecoin P2Pool status - http://p2pool.litecointools.com/
P2Pool wiki page - https://en.bitcoin.it/wiki/P2Pool
Mailing list for urgent news (updates, bugs) managed by Forrest V: http://groups.google.com/group/p2pool-notifications