In the ACTS-project DIANE (Design, Implementation and Operation of a Distributed Annotation Environment), a multimedia annotation system has been developed. One of it's greatest benefits over legacy multimedia authoring systems is it's simplicity. It enables users to create multimedia documents instantly without requiring great knowledge of programming languages or other details of the authoring system. Media can be integrated into annotations ranging from standard monomedia objects like audio, images, etc. to recorded application output from legacy applications. The client/server architecture has been implemented in a platform-neutral way using Java and it's extensions (e.g. Java Media Framework) and is running on either Internet/Intranet and broadband network technologies like ATM. This paper will present the architecture and the document model of DIANE with a focus on integrating custom user applications into multimedia annotations. A usage scenario will describe the system in general.