And X11 on Linux (if you're not using Wayland) supports middle-click emulation, where pressing the left and right mouse buttons simultaneously (debounced to within a couple milliseconds) will be interpreted as a middle-click.
I may or may not use this with my laptop dozens of times a day (it's how I copy/paste out of xterm).
(Fun bit of trivia, my old EliteBook 8470p has a trackpad+trackpoint setup with two independent sets of buttons, and while I don't seem to be able to middle-click with the trackpoint buttons, I can send a middle-click by pressing both trackpad buttons, keep them held down, and then independently send left and right clicks (press-release) using the trackpoint buttons as much as I want. I somehow doubt that was an accident. Engineering archaeology is fun :D)
I may or may not use this with my laptop dozens of times a day (it's how I copy/paste out of xterm).
(Fun bit of trivia, my old EliteBook 8470p has a trackpad+trackpoint setup with two independent sets of buttons, and while I don't seem to be able to middle-click with the trackpoint buttons, I can send a middle-click by pressing both trackpad buttons, keep them held down, and then independently send left and right clicks (press-release) using the trackpoint buttons as much as I want. I somehow doubt that was an accident. Engineering archaeology is fun :D)