There's also RethinkDB which seems to be focused on the D in acid while being a non-relational database. When you really need performance, in general relationships/joins need to go out the window as much as possible, and often one or more of the letters in ACID are compromised.

It should get very interesting in the next couple of years.. of course MOST environments don't need the kind of performance or scale that these systems are really offering.

IIRC StackOverflow ran for a very long time on a single server, under some pretty serious demand. In some cases SQL with a caching system for mostly-read data can be better... other scenarios tend to fit a document (non-relational) data store better.. just depends.