Phones are personal devices, so users expect their data to be local. But they are also collaborative devices, so users expect them to talk to each other. An occasionally connected Android application is the best of both worlds. It stores personal data locally for instant access. And it synchronizes with remote services for collaboration.
Correspondence is an open source library specifically designed to make it easy to build occasionally connected applications. When you design your data model using its DSL, it generates both a local database and a network protocol. Then it gives you an object model to code against that seamlessly bridges the two worlds.