Gimme a break. Macintosh has simple text, and you can probably write one in java. I mean, when learning a language, it’s the second program you make (after “Hello world”).
[EDIT=What’s the Linux equivalent? or does everyone write their own?]
Wow! I can’t believe noone mentioned emacs yet. I use emacs for everything. Granted that I mostly use perl (see cperl-mode in emacs), but if I used other languages, I’d use emacs for them as well. Emacs runs on pretty much anything I am pretty sure. The “unixes” are fine with it. There is also a windows version. It comes with many modes for different languages that include syntax high-lighting and other fun stuff. It also recognizes CVS files and has keys for cvs commands. A lot of people use emacs for a lot more. For example email and irc or whatever else one might want to do on a computer. Sometimes it is refered to as “editor and kitchen sink”.