Handy electrical devices
 

We made a device out of a momentary DPDT switch and one of those many 20 amp fuses we've collected over the years, which takes input from a battery and outputs using our favorite connectors, and allows you to drive a motor forward or backwards. It has been very handy in prototyping, as it cuts out the alligator clips (fire hazard) or the RC and OI (waste of programmers' time).

What similar items have you made or found?