Schemafree is a key/value store based on Mysql

Mulgara is a scalable RDF database written entirely in Java.

Memcachedb is a distributed storage system designed for persistence. We simply hacked from memcached and tugela. But neither of them. Memcachedb is not a cache solution, it is a persistent solution for high-frequency writing and reading. It conforms to memcache protocol(not completed, see below), so any memcached client can have connectivity with it. Memcachedb uses Berkeley DB as a storing backend, so lots of features including transaction and replication are supported.