I'm always amazed at the cool/useful new tools that I find out about when I talk to new people. It can be hardware or software. My current favorite, ferrule crimpers. Probably because I've been wiring a control cabinet.
Pretty tough to pick just one! But I will submit the humble but incredibly versatile CHP-170 cutters. It's a small pair of flush cutters, with about an inch of cutting surface and a slight angle.<p>The nominal purpose is for cutting leads of through hole components on a circuit board, but it's useful for pretty much any application where you need to cut something small and hard. (makes a great toenail clipper, for instance, lol).