We are presenting a software development framework called OSGART for Rapid Application Development (RAD) in the domain of Mixed Reality (MR). This toolkit is being developed as an extension to OpenSceneGraph [3]. It implements a hierarchical, scenegraph based approach to marker based AR using the AR Toolkit [4]. Due to its tight integration with OpenSceneGraph it provides a valuable test environment for bi-directional transition between immersive Virtual Environments (IVE) and Augmented Reality (AR).