I'm thinking about the use case to have a native app be able to work nicely with no internet connection, but then once the internet connection resumes, it downloads new data from the server and sends its offline-modified data up to the server.

From a quick search online [0] [1], I see people doing offline MongoDB sync using SQLite, but nothing like using Mongo directly. With CouchDB, we can use either the old Couchbase native app SDK, or the Cloudant native app SDK, to sync up nicely with a CouchDB instance in the cloud. We've had this running for awhile, and it works quite well, and we do not have to shuffle information to and from a SQLite database... at least, we're not doing it, since the Cloudant or Couchbase SDKs for iOS and Android keep track of all the data and store it on the mobile device however they'd like.

If there is anything similar for Mongo, I'd be interested to know!

[0] https://stackoverflow.com/questions/23623295/how-to-make-an-... [1] https://stackoverflow.com/questions/13295960/sqlite-on-andro...