Way back in the tube (valve) era, someone found that a mains frequency
 low voltage fed through a resistor and suitably connected to an oscilloscope
can  produce meaningful waveforms when connected to unknown components
 and circuits. This project does it without the inconvenient low voltage mains
transformer which is usually used. The "octopus" name comes from all
the cables which are hanging off it.

If you're interested in more info and maybe even building one, click here to
download the zip file which contains the documentation and PCB gerber files.