In Linux there is no end of decent text editors. There are probably a dozen popular ones, with dozens more languishing in obscurity.
For Windows I’ve found a decided lack of quality, free text editors. I rarely have need of one myself, but I frequently find people who need to edit some html, but don’t have a good way to do it.
I read about Notepad++ the other day, and then looked it up today to really read about it, and it looks great. Open source, using real ASCII text and not some OS proprietary character set, small, fast; it fits the bill for a good text editor.