It's a new fork from Steem. They are taking their snapshot today before Steem HF23 but I've heard conflicting stories on when the chain for Blurt will deploy. It was originally scheduled for July 4th but not sure if it's also been moved up.
I'm sure others can give a much better description of the differences than I can. That being said what I've been hearing is that it's focused on private property (everyone gets their property versus Steem stealing and Hive not airdrop) and that the chain won't have downvotes.