Simple as it may be at its core, Berkeley DB can be configured to provide concurrent non-blocking access or support transactions, scaled out as a highly available cluster of master-slave replicas, or in a number of other ways.
Berkeley DB is a pure storage engine that makes no assumptions about an implied schema or structure to the key-value pairs. Therefore, Berkeley DB easily allows for higher level API, query, and modeling abstractions on top of the underlying key-value store.
Berkley DB is used as the storage engine for MemcacheDB and is one of the pluggable engines for Project Voldemort.
Original title and link: Using Oracle Berkley DB as a NoSQL Data Store (NoSQL databases © myNoSQL)