(Apache) CouchDB is a peer based DISTRIBUTED database system.
Instead of storing data in rows and columns, the database manages a collection of (JSON) documents.
Apache CouchDB is a distributed, fault-tolerant and schema-free document-oriented database accessible via a RESTful HTTP/JSON API. Among other features, it provides robust, incremental replication with bi-directional conflict detection and resolution, and is queryable and indexable using a table-oriented view engine with JavaScript acting as the default view definition language.
Unlike SQL databases which are designed to store and report on highly structured, interrelated data, CouchDB is designed to store and report on large amounts of semi-structured, document oriented data. CouchDB greatly simplifies the development of document oriented applications, which make up the bulk of collaborative web applications.
It is designed for extreme scalability and is easily deployed to multi-core or multi-server clusters.
“Front-ends / APIs”:
CouchRest (ruby)
Couchdb-lucene
July 2010: CouchDB 1.0 released