Extensible, customizable GNU text editor.
GNU Emacs is an extensible, customizable text editor—and more. At its core is an interpreter for Emacs Lisp, a dialect of the Lisp programming language with extensions to support text editing.
The features of GNU Emacs include: content-sensitive editing modes, including syntax coloring, for a wide variety of file types including plain text, source code, and HTML; complete built-in documentation, including a tutorial for new users; full Unicode support for nearly all human languages and their scripts; highly customizable, using Emacs Lisp code or a graphical interface; a large number of extensions that add other functionality, including a project planner, mail and news reader, debugger interface, calendar, and more. Many of these extensions are distributed with GNU Emacs; others are available separately.