The MIT Lisp Machine had a version of Emacs written in Lisp called ZWEI and later called Zmacs. The Lisp Machine window system had tiling features in its windo

The MIT Lisp Machine had a version of Emacs written in Lisp called ZWEI and later called Zmacs. The Lisp Machine window system had tiling features in its window manager and also a split screen feature in ZWEI. The 1980 sources of the Lisp operating system had that, but it might have been developed earlier.