PouchDB is one of CouchDB's killer features. During development you can effortlessly switch between storing things locally, in the browser, and then sync with a remote database.

For native mobile apps, there are also a variety of native libraries that can be used:

Couchbase-Lite: https://github.com/couchbase/couchbase-lite-ios https://github.com/couchbase/couchbase-lite-android/

Cloudant Sync: https://github.com/cloudant/sync-android https://github.com/cloudant/CDTDatastore

We've had a good experience with CouchDB with an Android native app, iOS native app, and a web app (using PouchDB with it there).