CouchApps are JavaScript and HTML5 applications served directly from CouchDB. If you can fit your application into those constraints, then you get CouchDB’s scalability and flexibility for free (and deploying your app is as simple as replicating it to the production server).

There are also tools for deploying browser-based apps to JSON web servers and PouchDB is the future of browser based sync apps. It can sync with the same sync protocols but uses the built-in storage of HTML5.