OpenSeed is an opensource database. It also has some decentralized features in that anyone can run a node. It has features that will make building applications faster and easier and was built specifically with a lot of the problems that Steem faces in mind. For example...
- User accounts
So on Steem to make a new account, we have to make a blockchain level account which is slow and cumbersome, but with OpenSeed you could make accounts as easily as other centralized services.
- Chat
Chat is fast and not necessarily something you want to be public. OpenSeed allows you to make something private, something that can be deleted, basically all the things you expect with a chat client. Only it can be integrated into Steem dapps across the board with a consistent experience.

Everything it does is along these lines. All the things that social applications need, but that either doesn't require or doesn't work on a blockchain, OpenSeed is there to fill those gaps.