CouchDB

Apache CouchDB, commonly referred to as CouchDB, is an open source document-oriented database written mostly in the Erlang programming language. It is part of the NoSQL group of data stores and is designed for local replication and to scale horizontally across a wide range of devices. CouchDB is supported by commercial enterprises Couchbase and Cloudant.

CouchDB is a document oriented database that can be queried and indexed using JavaScript in a MapReduce fashion. CouchDB also offers incremental replication with bi-directional conflict detection and resolution.

Couchbase is the leading provider of NoSQL database technology, powering some of the world’s largest web applications. Whether a corporate e-commerce system, a blockbuster social game or the world’s largest online advertising system, Couchbase offers a more flexible, scalable and cost-effective approach to data management than traditional database solutions.
A document database server, accessible via JSON API.
Ad-hoc and schema-free with a flat address space.
Distributed, featuring robust, incremental replication with bi-directional conflict detection and management.
Query-able and index-able, featuring a table oriented reporting engine that uses JavaScript as a query language.

External References
http://en.wikipedia.org/wiki/CouchDB
http://www.ibm.com/developerworks/opensource/library/os-couchdb/index.html
http://couchdb.apache.org/
https://cloudant.com/
http://www.couchbase.com/