The key with Emacs is that it's an editor that grows: the close mapping between the editor and its code makes it more fluid and natural to extend than any other popular tool I've tried. It's a fuzzy distinction—not something you can put on a feature checklist—but it's made working with Emacs qualitatively different from working with other tools. While Emacs has certainly influenced other editors, none of the ones I'm familiar with have carried over this core philosophy.