Emacs is a nice operating system — it just lacks a good editor.
A programmers' text editor and IDE. See emacs(1).
Its icon is a kitchen sink, and there's very good reason for that. Its core is an Elisp interpreter which can be used to implement extensions, of which literally hundreds have been written — including a complete WebBrowser, MailClient, NewsReader, and almost anything else you could (n)ever need, to the extent that many Emacs users never really use another application.
A young man studying in the temple went seeking the priest. He asked the priest “Master, does Emacs possess the Buddha nature?” The priest had resided in the temple for a good many year, and was very wise. He thought for a while, and then answered: “I don’t see why not, it’s got bloody well everything else.” The young man then achieved enlightenment shortly after.
Unix programmers tend to settle on either Emacs or vi as their main programming environment, then pick on each other for their choices.
For a decent introduction to using Emacs, look at our slides on the UnixTutorials page.
If you are having trouble with copy&paste in Emacs (or XEmacs) under X11, check this quick tip.