An emacsen editor for the MIT Artificial Intelligence Lab Lisp machines written by DanielWeinreb? and MikeMcMahon? in the early 1980s. ZWEI is the acronym for “ZWEI Was EINE, Initially”. Later ZWEI was renamed and further developed as Zmacs.
Technical improvements made by ZWEI included being programmable with Lisp, and representing an editing buffer as a doubly-linked list of lines.
Sources to ZWEI and the MIT CADR LispM? from 1980 are available here: http://www.heeltoe.com/retro/mit/mit_cadr_lmss.html