I am one of the original CouchDB folks, and a cofounder of Couchbase. We have spent the last few years quietly building an enterprise-class suite of Couch sync compatible databases. Everything we do is open source and Apache licensed.
[edit] we've been able to do this, funded by the success of Couchbase Server. Which looks like a high-performance NoSQL database, not an offline mobile database, but it uses many of the same data structures.
Couchbase Mobile is native on iOS, Android, and C#, and compatible with PouchDB and Apache CouchDB. http://developer.couchbase.com/mobile
Here is an example of how General Electric is using our open source platform to power the Internet of things. http://www.couchbase.com/nosql-resources/presentations/offli...
[edit] we've been able to do this, funded by the success of Couchbase Server. Which looks like a high-performance NoSQL database, not an offline mobile database, but it uses many of the same data structures.