A synchronization system provides a generic synchronization mechanism in which copies of data of an entity maintained by different applications can be synchronized through application-specific entity adapters. An entity adapter for an application receives from the synchronization system a synchronization request to synchronize an entity of the application and interacts with the application to ensure the entity is synchronized as requested. Each application that takes an action on an entity provides a transaction to the synchronization system. Upon receiving a transaction, the synchronization system stores an indication of the transaction in a synchronization store. The synchronization system waits until any sent synchronization transactions for an entity complete before sending subsequent synchronization transactions for that entity to ensure that the same transaction ordering is used by the target applications.