Emacs

From the GNU Emacs project page:

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.

Emacs is a great text editor for people who want to be able to customize every single thing about their editor. Some helpful Emacs resources:

• The Emacs Wiki can probably answer any question you have
• Planet Emacs is a great blog article aggregator
• Join the #emacs IRC channel on freenode
• Emacs is thoroughly documented

You may also want to take a look at the text editors topic.

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