FoundationDB is a distributed transactional key value store. It exposes transactions across complete key space. API provided on FoundationDB KV Store is low level and minimalistic - you can do set, get, getRange in transactions. This gives lot of flexibility to build different data models on top, which are called layers.
Based on the implementation of layer, FoundationDB can match features of some of the databases you mentioned above. Some of the layers being discussed in the forums now
- SQL Layer being discussed here
- Document Layer being discussed here
- Block Layer
You can split tasks of all the databases you mentioned above into two parts
- Data model (SQL, Document, Column families, KV Store etc)
- Scalability, some or all of ACID guarantees
With the way FoundationDB is designed you can depend on FoundationDB core for Scalability and ACID guarantees, then create/use a layer of your liking for the data model. @wwilson did better job than me putting the same in words here