Note that Emacs and GNU Emacs are different things. Emacs is a family of editors, which share some basic design principles (buffers, keymaps, modes, extended co

Note that Emacs and GNU Emacs are different things. Emacs is a family of editors, which share some basic design principles (buffers, keymaps, modes, extended commands, ...). Why do you think Lisp IDEs look like some Emacs? Because you happen to know them and haven't seen the other ones. Many Lisp IDE's have an Emacs editor, but are not based on Emacs. For example the MIT Lisp Machine has Zmacs, but that's mostly used for editing text (and some functionality around it). Zmacs is also used as a component in a few other programs, like the Mail client. Other than that most Lisp Machine programs are neither based on Zmacs nor have a Zmacs UI. Examples: file browser, font editor, terminal, Lisp repl - none of that feels/looks like Emacs. Interlisp-D / Medley from Xerox didn't look like Emacs at all. The Allegro CL IDE doesn't look like Emacs. LispWorks uses an Emacs written in Common Lisp, but for example does not share the buffer handling (in LispWorks buffers have their own windows all the time and they can't be changed). Additionally much of the LispWorks IDE is not based on an editor paradigm (inspectors, debugger, preference windows, ...). Since 15 years most (not all) open source CL developers used GNU Emacs + SLIME as the IDE. SLIME replaced older tools for GNU Emacs. There wasn't much competition for SLIME - it also was relatively easy for Lisp programmers to add IDE features to an editor extensible in some Lisp dialect - it's much more difficult and more difficult to make Eclipse or Intellij a decent Lisp IDE, and the results so far are clunky. SLIME OTOH is quite usable as a Lisp IDE. It would be about time to have a better Lisp IDE than GNU Emacs / SLIME - especially one which is more graphical. But then, we now have the javascript web and GUIs are again different.