CouchDB is a NoSQL database for storing JSON documents. It comes with a REST API out of the box so your client applications can persist data while requiring you to write little or no server-side code. CouchDB's killer feature is its ability to easily replicate, which allows for horizontal scaling, easy backup, and for client adapters to synchronize documents. This is perfect if you want to write an application that is offline-first. It's become my go-to database when creating new