To maintain availability and responsiveness, mobile applications sharing data often work on their own copy and transmit their local changes to other participants. Existing systems for recording, transmitting and reconciling concurrent changes are usually ad-hoc and specific to particular applications. In contrast, we present Joyce, a general application programming framework for creating highly dynamic mobile, collaborative applications. The framework abstracts application semantics using an action-constraint formal model and provides communication and consistency services based on this model. The framework exposes an interface that allows application programmers to concentrate on core functionality without worrying about these issues. Applications made with the framework can run seamlessly across changing combinations of devices, users and synchrony. We discuss the principles behind the framework, its implementation and evaluate its utility by implementing a complex, shared application.