My favorite feature from the past is RISC OS's "adjust" feature, bound to the third mouse button. This had three functions: Selecting menu items without closin

My favorite feature from the past is RISC OS's "adjust" feature, bound to the third mouse button. This had three functions: Selecting menu items without closing the menu. Toggling selection status of selectable icons (same as control+click in modern GUIs). Changing the length of text selections (same as shift+click in modern GUIs). Sadly, modern GUIs seem to limit themselves to two mouse buttons. Adding "adjust" would improve productivity if you had a three button mouse, and you could ignore it if you lacked mouse buttons and not be any worse off. Maybe there are other good features from early OSs we have forgotten.