I have a special section in my shed for tools that are designed to do one annoying and fiddly job really well. There's the fork seal driver, which is exceptionally useful for gently bashing rubber seals into fork boots, and utterly useless for anything else. There's the chain tool, which presses motorcycle chain plates together and peens over the rivets on them, and I'm knackered if I can find anything else it's good for. There's the two-foot torque wrench, which is used exclusively to bludgeon stuck front sprocket bolts and otherwise entirely ornamental.
So here's another single-use tool – one that will be extremely handy for a very small subset of people, but will likely not rise above the threshold of "heh, look at that" for the average home handyman.
Quadsaw cuts square holes in plaster walls. That makes it very handy for installing power points, light switches and other electrical bits and pieces, and … not much chop for anything else.
It smashes that job, though. Connecting to the end of a drill, Quadsaw can be set to drill squares or rectangles with its four straight cutting blades. It's got a height gauge (a stick you can elongate to make sure all your switches are at the perfect height) and a built-in spirit level to keep things straight.
It makes one annoying and fiddly job much quicker, cleaner and easier. According to the Quadsaw people, electricians cut 200 million square holes in walls a year, in the United Kingdom alone. Moving to Quadsaw makes these things so much faster that at an average worker pay of UK£20 per hour, this thing could save the British building industry a whopping UK£320 million per year.