Despite sharing a common name, Couchbase and CouchDB have very little in common. It was a bad move by the original developers of CouchDB that left the project to give Couchbase the name Couchbase.
Couchbase was designed for write-heavy applications and built with clustering in mind from day one. CouchDB was designed for read-heavy applications where versioning and replication are important. Cloudant, by way of their BigCouch product, has done a lot of great work on clustering for CouchDB and all that work is slowly making its way into CouchDB core.
Couchbase was designed for write-heavy applications and built with clustering in mind from day one. CouchDB was designed for read-heavy applications where versioning and replication are important. Cloudant, by way of their BigCouch product, has done a lot of great work on clustering for CouchDB and all that work is slowly making its way into CouchDB core.
If you want the comparison of CouchDB vs Couchbase from Couchbase directly, you can read that here: http://www.couchbase.com/couchbase-vs-couchdb
In my opinion, the next closest NoSQL DB to CouchDB would be ElasticSearch.