MySQL :: MySQL Document Store
"Native JSON Document Storage - MySQL provides a native JSON datatype is efficiently stored in binary with the ability to create virtual columns that can be indexed. JSON Documents are automatically validated."
Is Postgres NoSQL Better Than MongoDB? | Aptuz Technology Solutions
PostgreSQL, the NoSQL Database | Linux Journal
"One of the most interesting new developments in PostgreSQL is that of HStore, which provides a key-value store within the PostgreSQL environment. Contrary to what I originally thought, this doesn't mean that PostgreSQL treats a particular table as a key-value store. Rather, HStore is a data type, akin toINTEGER, TEXT and XML. Thus, any column—or set of columns—within a table may be defined to be of type HSTORE"