Zettlr is quite nice. The UI has a few quirks and sometimes does not follow conventions set by other applications, but the wysiwyg interface for markdown offers a great editing experience. And because it is all just markdown files in local disk there is no vendor lockin.

I am not the primary intended audience, but I wrote my last sci-fi novel (The Grandmaster's Gamble) entirely using Zettlr and pandoc. The built-in languagetool integration was a big help.