A fun weekend project was creating this surface scanning tool for CNC machines. I use Estlcam (thanks @ChristianKnull for this excellent software!) and this tool enables me to use surface scanning functionality without using conductive tape.
You can read about the project here and find links for downloading the files:
DIY GARAGEPROJECTS - PROBE TOOL
Probe tool in action: https://www.youtube.com/watch?v=XWPMjJfk6uw