"What CouchDb is:

• * A stand-alone document store, accessible via XML REST.
• * Ad-hoc and schema-free with a flat address space.
• * Distributed, featuring robust, incremental replication with bi-directional conflict detection and resolution.
• * Query-able and index-able, featuring a table oriented reporting engine with a simplified formula query language.

The CouchDb data model was partially inspired by the Lotus Notes and Domino backend."

Update: Harry Fuecks at SitePoint - CouchDb: document oriented persistence.