Monero (XMR) is a cryptonight algorithm based alternative crypto currency. The coin is based on Proof of Work and has a block reward that varies smoothly. The difficulty retargets every block with a sixty second block target.
Monero uses a Ring Signature system to protect your privacy, allowing users to make untraceable transactions.
Privacy (Untraceable payments, Unlinkable transactions) Monero daemon uses the original CryptoNote protocol except for the initial changes (as the block time and emission speed). The protocol itself is based on ring signatures (Daniel J. Bernstein's Curve25519 + Ed25519, Schnorr signatures on a Twisted Edwards curve) and stealth addresses. The end result is passive, decentralised mixing based on heavily-tested algorithms.
Decentralisation The smart mining forthcoming feature will allow transparent CPU mining on the user's computer, far from the de facto centralization of mining farms and pool mining, pursuing Satoshi Nakamoto's original vision of a true p2p currency.
Scalability Monero has no hardcoded limit, which means it doesn't have a 1 MB block size limitation preventing scalability.