3-button mouse operation seems underused in modern OSes. I miss the "adjust" mouse button in RiscOS. It made changes with the minimum possible state change, eg.

3-button mouse operation seems underused in modern OSes. I miss the "adjust" mouse button in RiscOS. It made changes with the minimum possible state change, eg. adjust-dragging a window would move it without changing the z-order, and adjust-clicking menu items would click the menu item without closing the menu.