POS 3.0 or "Proof of stake protocol 3", it advances on Blackcoins protocol 2  that is one of the most secure and used protocol for proof of stakes coins. POS 3.0 will be more secure and stable and one thing that stands out is no need for coinage as coins will be staked based on confirmations, it's still a work in progress and when the final specs are out we are ready to go, we will have a separate branch at github for protocol 3 and work from there.