Autodesk shipped its free iOS (iPhone, iPad, or iPod) based ForceEffect program several months ago, and it was an instant hit, especially with students and makers. It allowed users to do static free body diagrams, in a most elegant way.
Autodesk has just released ForceEffect Motion. It too is free. It appears to be a phenomenal tool for doing conceptual design of kinematic systems. And probably a great excuse to ask your boss to buy you an iPad.