What about the liberal? Now that's a real tool if I ever saw one. (^_^)
My favorite tool of all time is the simple pocket knife. Used it more than any single one of the items on my pegboards or in the rollaway. Certainly not useful for everything, but I find it the most useful overall. So much so that it is the one item that has ever got me in trouble in my life. I've had a pocket knife in my right front pocket every day fo my life since I was six years old. The style and or features have changed over the years, but it is always there. Ready to whip out when it's needed. And I've whipped it out a LOT.
I've whipped it out in a wedding (my own in fact).
I've whipped it out in every room of every house I've ever lived.
I've whipped it out changing a tire.
I've whipped it out feeding the dog.
I've whipped it out milking a goat
I've whipped it out cooking meals
I've whipped it out in front of my mother-in-law
I've whipped it out in front of my minister
I've whipped it out in front of police officers
I've whipped it out in front of a guy who runs a porn shop
I've whipped it out for gay and straight both
I've whipped it out in front of my English teacher because I was damned if I'd waste that period writing a paper rather than watch some boring filmstrip and flirt with Dawn in the dark.
I've abused them in ways the designers never imagined or recommended. I've broken more than I've worn out. I've had them confiscated by principals, French security, and TSA agents, but I feel naked without it.
May not be the tool that changed the world, but as far as usefullness, none compare.