I could have sworn I saw a dropdown command/search dialog designed by Jeff Raskin as part of The Humane Interface, and demonstrated in PyTHE a Python imeplementation of it.
Can't find any evidence of it, but I can find a 2003 Guido van Rossum review of Jeff Raskin's book "The Humane Interface" in which Raskin mentions LEAP(r) a design for adding search-backwards and search-forwards keys below the spacebar to save people from arrow keys and mouse use, which is demonstrated on the CanonCat computer from 1987 in this[2] video on YouTube.