pcb-rnd-3dview is a small glue layer that can "integrate" an external 3d view window in pcb-rnd. It really is a user script and a file watch wrapper around projector(1).
That script exports the current board in projector format then runs the watcher in the background. The watcher runs projector on the exported file and reloads the file if it changes on disk, so that subsequent exports from the script will automatically update the 3d view.
For more information on dependencies, installation and how to use it, please read file INSTALL in the source release.
Move the mouse horizontally or vertically while the right mouse button is pressed and the board will be rotated around the X and Y axes; with the left mouse button around the Z axis. The middle mouse button (often scroll sheel press) the object can be panned along the X and Y axes. Scroll wheel rolling up or down will change the zoom.
Pressing 'q' will quit. Pressing a key between 1 and 6 will set a default view angle (top, bottom, side, etc.)