I am the Chief Software Architect at Simbios. My primary job is to design, develop, and promote an architecture for SimTK that achieves the broad vision set out in the Simbios grant proposal. I am also the lead developer of Simbody, the SimTK multibody dynamics package. I am a computer scientist by training, with a 25 year professional career in operating system development, high-performance computing, software for simulation of mechanical systems (including biomechanical), software for simulation of biomolecules, and physics-based computer games and virtual worlds. I have been designing, building, managing and selling software for physics-based simulation since 1980 and co-founded two companies, Symbolic Dynamics and Protein Mechanics. SimTK is my fifth or sixth simulation framework design, depending what you count. Most of my earlier ones are still in production use and I hope to be able to say the same about SimTK in 10 or 20 years.