This paper proposes Commutative Event Sourcing as a simple and reliable mechanism for model synchronisation, bidirectional model to model transformations, incremental updates, and collaborative editing. Commutative Event Sourcing is a restricted form of a Triple Graph Grammar where the rules or editing commands are either overwriting or commutative. This restriction gets rid of a lot of Triple Graph Grammar complexity and it becomes possible to implement model synchronisation manually. Thus, you are not restricted to Java as your programming language and you do not need to use a proprietary library, framework, or tool. You do not even have to dig into graph grammar theory.