Gosling Emacs (often shortened to "Gosmacs" or "gmacs") is a discontinued 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 any 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. Among other things, he rewrote part of the Gosling code headed by the skull-and-crossbones comment and made it "...shorter, faster, clearer and more flexible."
In 1983 UniPress began selling Gosling Emacs on Unix for $395 and on VMS for $2,500, after renaming it Unipress Emacs. Controversially, it 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 (since August 2004) do not feature the skull-and-crossbones warning.