Check out https://github.com/GetPublii/Publii
However, I'm looking for something that's less of a local CMS, and more of just... a document editor which can open up HTML files, edit them with a GUI interface, and save them somewhere.
Ideally, it would be an editor like Sublime, where you can drag a folder containing HTML files in there (so you can navigate folders and access other files & content), and edit visually...