I've seen Enter, Shift-Enter, Ctrl-Enter, and Alt-Enter, (and on macOS, Cmd-Enter and Option-Enter), depending on the application. Total circus. I think this is actually a weakness of the standard keyboard: Keyboards should at the very least separate "submit form / enter" from "newline / carriage return" with different physical keys, but good luck changing that one, given the strong legacy of combining these functions.