A synchronization framework is provided for synchronizing data groups between a server and clients that may go off-line. The framework includes a client sync provider component that interfaces to client storage in a storage format independent way, a sync agent component that collects synchronization metadata maintained by the clients and uploads and/or downloads changes to the data groups to and/or from server storage and a server sync provider component that interfaces via sync adapters to server storage independently of storage format. The framework provides default building blocks for building off-line synchronizing applications that behave according to default application synchronization scenarios, and also enables custom building blocks for custom off-line application synchronization scenarios.