emacs is another, larger editor that comes with most standard systems. It has many features not found in other editors, not to mention a built-in LISP interpreter. Because of its many features, many of the emacs commands are multiple control or escape sequences. Some of the more common are listed below:
emacs can be used to edit several buffers at one time, and provides many different ``source'' environments helpful to creation of source code. These areas are far too broad to be covered in these few paragraphs. The Tutorial is highly recommended as a good way to get to know the features of emacs. The info pages will give other, useful information not found in the tutorials. Both of these should be enough to give you a good feel for how this editor works, and what it can provide.