How many database systems there are that use JSON for storage or transport? I know of:
I remember I saw yet another vendor in a SO user's profile. That systems was using what they called binary JSON, but I can't remember the name of the product.
Lately, it appears that more and more DB projects are looking towards JSON for persistence storage. Some of them are even embracing HTTP as a transport layer.
MongoDb is the one that uses a binary JSON storage format. I don't know if there is another that is document oriented. Most of the others are key value stores and can only retrieve an object based on one key.