I was the Chief Software Architect at Simbios. My primary job was to design and develop an architecture for SimTK that achieves the broad vision set out in the Simbios grant proposal. 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. I have been designing, building and selling software for physics-based simulation since 1980 and started two companies. SimTK was  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.