Complex sentence: Richard Stallman's now-famous Emacs editor was originally implemented in TECO (later versions of Emacs, first Multics Emacs and then GNU Emacs, were implemented in Lisp and C/Emacs Lisp), respectively.
Split into simpler sentences: Richard Stallman's now-famous Emacs editor was originally implemented in TECO. Later versions of Emacs, first Multics Emacs and then GNU Emacs, were implemented in Lisp and C/Emacs Lisp, respectively.