CouchDB is a distributed, document-oriented, Non-Relational DataBase Management Server (NRDBMS). It is accessible via a RESTful JSON API, and provides incremental replication with bi-directional conflict detection and management. Data is stored with a schema-free, flat address space, and may be queried via a table-oriented reporting engine that uses Javascript as a query language.
WWW: http://couchdb.apache.org/