- CouchDB is a document-oriented NoSQL database that uses JSON documents and RESTful APIs. It features schema-free design, incremental map-reduce views, and multi-directional replication. - Views in CouchDB allow querying and aggregating documents using JavaScript map/reduce functions. Documents can be indexed and searched by mapping words to document IDs. Results can also be reduced to counts. - Replication in CouchDB allows databases to be copied or continuously synchronized across installations. Replication can be filtered to select specific documents.