Lem is an Emacs-like editor built in Common Lisp. It's very impressive and usable for its age and I can see why some people see it as a better Emacs. Still has nowhere near the mindshare of Emacs, though, and it has a long way to go before it can match the Emacs ecosystem.
It doesn't. There is a terminal frontend, a web rendering frontend, and a deprecated SDL frontend. The web frontend was explicitly developed to speed up development, writing implementations for graphics described in CL (the part being accelerated) that can be later served by another frontend should some technical need emerge. Anyone acting like this is Electron is either leaping to conclusions or being intentionally misleading.
