Panda3D was originally developed by Disney. Open sourced and now jointly is supported by Disney and the Entertainment Technolgoy Center (ETC) at Carnegie-Mellon (CMU). The website includes screenshots and videos of the what can be built with this tool. For the virtual worlds work at CMU, this has replaced Alice for creators with a programming background. Most of the work you will see on the website is very entertainment oriented (the focus of the ETC) but I think some interesting "serious sims" could be built with this tool as well.