Abbreviated menu button (OPEN LOOK)
OPEN LOOK's compact menu button: a small square with a downward triangle and no label, for places where a full labelled button would not fit.
In OPEN LOOK an ordinary menu button carried a label and a small triangle, the menu mark, signalling that it opened a menu rather than doing something. The abbreviated version dropped the label and kept only the mark inside a square frame. It usually sat next to a text field or a value showing the current choice, and pressing MENU, the right mouse button, dropped the options down beneath it — effectively what everyone later called a combo box.
The same little button sat in the left corner of every window header under olwm, opening the window menu. XView and OLIT both shipped it as a ready-made component. The idea outlived OPEN LOOK comfortably: a small down arrow next to a field is still the universal sign that there are more options to unfold.