http://memcachedb.org/

http://code.google.com/p/scalaris/

http://couchdb.apache.org (and the Java client lib at http://code.google.com/p/couchdb4j/)

http://groups.google.com/group/couchapp?pli=1

http://aws.amazon.com/simpledb/

http://labs.google.com/papers/bigtable.html