Monero (XMR) is a new privacy-centric cryptocurrency based on the CryptoNote protocol.
Monero is competing directly with coins like Darkcoin, AnonCoin, and LibertyCoin in solving the problem of making digital cash transaction anonymous.
CryptoNote features an entirely new code base and is not a fork of Bitcoin. More info about CryptoNote can be found at their website https://cryptonote.org/
CryptoNote uses Ring Signatures to conceal sender identities via mixing and it also has unlinkable transactions that is achieved using 1-time keys for each individual payments.
CryptoNote should not be confused with CoinJoin. Although they are both aiming to make digital transaction anonymous, they are two entirely different implementation.