That, and the fact that it's very easy to extend it with Emacs Lisp. I know that it's possible to write extensions for most of the IDEs or text editors out ther

That, and the fact that it's very easy to extend it with Emacs Lisp. I know that it's possible to write extensions for most of the IDEs or text editors out there, but the degree of customization is higher with emacs, mainly because emacs is basically couple of primitive functions written in C + a lisp interpreter (also written in C) and the rest is written in lisp, so you have access to everything emacs has to offer if you want to customize it.