Gosling Emacs (often shortened to "Gosmacs" or "gmacs") was an Emacs implementation written in 1981 by James Gosling in C. Its extension language, Mocklisp, has a syntax that appears similar to Lisp, but Mocklisp does not have lists or any other structured datatypes. Gosling initially allowed Gosling Emacs to be redistributed with no formal restrictions, but later sold it to UniPress.
Gosling Emacs was especially noteworthy because of the effective redisplay code, which used a dynamic programming technique to solve the classical string-to-string correction problem. The algorithm was quite sophisticated; that section of the source was headed by a skull-and-crossbones in ASCII art, warning would-be improver that even if they thought they understood how the display code worked, they probably did not.
Since Gosling had permitted its unrestricted redistribution, Richard Stallman used some Gosling Emacs code in the initial version of GNU Emacs. UniPress began selling Gosling Emacs (which it renamed Unipress Emacs) as a proprietary product, and controversially, asked Stallman to stop distributing Gosling Emacs source code. UniPress never took legal action against Stallman or his nascent Free Software Foundation, believing "hobbyists and academics could never produce an Emacs that could compete" with their product. All Gosling Emacs code was removed from GNU Emacs by version 16.56, with the possible exception of a few particularly hairy sections of the display code. The latest versions of GNU Emacs (as of August 2004) do not feature the skull-and-crossbones warning.