Free, but use at your own risk. There is no warranty expressed or implied with these plug-ins.
This is a channel driver for the older Polhemus 3-Space. Includes source code and driver for Windows NT: Isotrak
SelectConnect
This is an immediate effect that tags all vertices that are physically connect to any tagged vertex in a polygon mesh. We use it to break apart imported .dxf and .obj models. It a Windows NT dll with source code included: SelectConnect