My own blogging/braindump platform, since I designed it for myself. I enjoy of working on it simultaneously with using it. I also use it for planning its own development.

I like using Word 97 for writing because of how fast it is, and how little it gets in my way. (I turned off Clippy, as much as I like him.)

Hacker News is very nice, too.

And, of course, the GNU/POSIX environment as a whole and command line in general.