EMACs is a free customizable text editor which was created, initially, as a part of the GNU operating system. The editor not only allows text editing but is also a great application for programming in the LISP programming language. Some of the features of EMACs are as follows:

"#Content-sensitive editing modes, including syntax coloring, for a variety of file types including plain text, source code, and HTML.

1. Complete built-in documentation, including a tutorial for new users.
2. Full Unicode support for nearly all human languages and their scripts.
3. Highly customizable, using Emacs Lisp code or a graphical interface.
4. 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."http://www.gnu.org/software/emacs/

"Extraordinarily powerful text editor with additional features including content sensitive major modes, complete online documentation, highly extensible through Lisp, support for many languages and their scripts through its multilingual extension, and a large number of other extensions available either separately or with the GNU Emacs distribution. Runs on many different operating systems regardless of machine.

It offers true Lisp, smoothly integrated into the editor, for writing extensions and provides an interface to the X windows system."http://directory.fsf.org/project/emacs/

• Extended Text Editor