Notepad++ on Windows, Vim & Geany on Linux. Both of those should run on Windows as well but as Vorticity said Vim is an aquired taste (but powerful editing potential lies with its steep learning curve).
If your looking for an operating system that also happens to have text editing features there's also emacs. (Tl;dr explanation: real versions of emacs are text editors implemented to a large degree in a dialect of lisp, if you can wrap your brain around Lisp then you can make it do nearly anything.)
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Will the transhumanist future have catgirls? Does Japan still exist? Well, there is your answer.
If your looking for an operating system that also happens to have text editing features there's also emacs. (Tl;dr explanation: real versions of emacs are text editors implemented to a large degree in a dialect of lisp, if you can wrap your brain around Lisp then you can make it do nearly anything.)
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Will the transhumanist future have catgirls? Does Japan still exist? Well, there is your answer.