This paper provides an overview of the Ambulant Open SMIL player. Unlike other SMIL implementations, the Ambulant Player is a reconfigureable SMIL engine that can be customized for use as an experimental media player core. The Ambulant Player is a reference SMIL engine that can be integrated in a wide variety of media player projects. This paper starts with an overview of our motivations for creating a new SMIL engine, then discusses the architecture of the Ambulant Core (including the scalability and custom integration features of the player). We close with a discussion of our implementation experiences with Ambulant instances for Windows, Mac and Linux versions for desktop and PDA devices.