Not a useful note and more of a personal opinion then factual, but beyond the inventors of the Internet or any hardware has to be the following notion from IBM:

a 1976 research report by Lance A. Miller and John C. Thomas of IBM, noted that "It would be quite useful to permit users to 'take back' at least the immediately preceding command (by issuing some special 'undo' command)."
Source: Behavioral Issues in the Use of Interactive Systems.

If you've guessed it, my vote goes for whoever invented the "Undo" button: cross-platform, multi-lingual, future-proof and as everlasting as human error.


More?
"By [undoing] repeatedly, you can gradually work your way back to a point before your mistake. This is convenient if you've made a mistake four or five commands back. It is marginally useful if you've made a mistake twenty or thirty characters back. And it is completely useless if your mistake is ancient history." - Learning GNU Emacs (page 42)

Undoing can itself be undone. After having undone an action, you can redo it... - Docs.Gimp.Org

Synonym: redound

Latin - Etymology - From unda ("a wave")