Windows: What's the most popular and powerful editor on Windows among text aficionados? Notepad++, by a hefty margin. Want something a smidge less menu-rich and, well, different? Notepad GNU is a very clever, open-source alternative.
Notepad GNU has a lot to recommend on its own, including optional background transparency, loads of HTML and other code-minded plug-ins, a menu that can quickly send a file to a browser or other app (even Notepad++), and all that text tweaking tools you need without the Office integration nonsense you don't. It doesn't offer everything that Notepad++ does, but that's kind of the point — it's a different layout and setup, and one newcomers might find pretty useful.
The one drawback, for English speaking users at least, is the hit-and-miss translation of some of Notepad GNU's more obscure features. You'll be able to grope your way around in the linguistic dark, most likely, but if you speak Russian and like the app, by all means — offer to help with the translation.
Notepad GNU is a free download for Windows systems only. It comes packaged in a RAR container, oddly enough — you can easily unpack it for free using 7-Zip.