ZWEI (ZWEI Was EINE, Initially, also German: two) was an early (~1980s) Emacs-like text editor written by Daniel Weinreb and Mike McMahon for the Lisp machine. It is the successor of the editor EINE (which is the feminine of a/one in German). Innovations by it include programmability in Lisp, and a new and more flexible method of internally representing buffers. It would later become Symbolics' editor of choice for its Lisp machine development environment, Zmacs. ZWEI is the editor library used for Zmacs (the editor), Zmail (the mail client) and Converse (a message client) in the Symbolics Genera operating system.