It's too early to say much about these apps yet, since the ideas so far are mostly just my own, and I haven't discussed with other developers much yet.
As far as the smart contract engine goes, it's basically just what it sounds like: the ability to run sandboxed smart contracts written in SQL on HAF servers that decide to support the smart contract processor. For example, the smart contract engine would allow the creation of token-management contracts (i.e. ability to create new types of tokens).