Edwin
Edwin an Emacs-like editor programmed by some of the guys who maintain the MIT-Scheme programming language, which is (I think) the original implementation of the Scheme programming language developed by Gerald J. Sussman and Guy Steele (or a predecessor of it). To this day, MIT-Scheme continues to be one of the fastest Scheme implementations, producing extremely efficient binaries for a high-level language.
It is Emacs-like in nature, except instead of scripting it in Emacs Lisp, you use Scheme. Unlike Emacs, there are very few extensions available for it, so no Org-Mode, no Magit, no nice themes. The GUI version of it is so antiquated, it uses its own widget toolkit that is similar to the Athena Widget Toolkit.
Although I use Emacs for everything, I still love Edwin just because I like Scheme as a language better than Emacs Lisp. I wish I had more free time, I would like to help modernize Edwin. Although at this point it would probably easier to write a whole new Emacs-like editor using Guile Scheme instead, since there is a very active user community around Guile Scheme, especially among the Guix OS clique.