EdWin is part of MitSlashGnuScheme. It’s a remarkably Emacs-like editor written entirely in Scheme. Early editions of the MIT Scheme User Manual listed the differences between Emacs 18 and Edwin.

Some time ago, the MIT student MattBirkholz implemented enough of Emacs Lisp to have Gnus run within Edwin.

CategoryExtensionLanguage EmacsImplementations