Can we take a moment to thank the folks at Apple for TextEdit? I’m serious. There is no shortage of text editors for OS X, yet I find myself continually coming back to TextEdit. It’s fast, simple, open source 1, and every Mac has a copy preinstalled. Pick out a nice monospaced font, and I think you have a challenger for even the most minimalistic of writing interfaces.
Apple’s OS X apps tend get a lot of criticism, but after 10 years and tens of thousands of words, I have yet to have a major issue with TextEdit. For getting thoughts to screen, it just works, and I think that deserves some public praise.