• https://github.com/apache/couchdb-nano - officially maintained by the Apache CouchDB team 
  
  
• https://github.com/IBM/cloudant-node-sdk - IBM Cloudant's Apache 2 licensed official client library that is also compatible with Apache CouchDB
• https://github.com/pouchdb/pouchdb (can be thought of as a client)
  
  

Older and/or outdated clients:

• https://github.com/cloudant/nodejs-cloudant
• https://github.com/tmpfs/rlx
• https://github.com/flatiron/cradle
• https://github.com/benoitc/noddycouch/