I've written twice now about the Windows application Smartdown (a Mac version is also available now). It's a markdown editor that includes code "folding" -- the ability to hide or "collapse" text under a heading. It is also "Zenware" -- software that adheres to a simple, stripped down aesthetic. It sells for $20 from Aflava. When I was on my writer retreat, I decided to buy it, first because it's a fine tool, second because good programmers should be paid. Smartdown is a pleasure to use, although I did have to reach out to support to figure out how to change its "save to panel" properties, instead of the more common minimize behavior. Smartdown can also be stored on a flash drive to make a portable application. I found it ideal for working with a long, chapter-length file, collapsing and expanding the sections to track the flow of it.
On my Linux box (a recycled ThinkCentre PC running LXLE) I already had HarooPad, which is free, but I sent them a donation, too. It too is a minimalist markdown editor with folding. It isn't quite as polished as Smartdown. In particular, HarooPad lacks spellcheck. But it offers GitHub markdown, which means it does Tasks - nice for a floating window with a list of things to be done for the day, and which allows for the satisfying ability to check them off as done. HarooPad runs on Windows, the Mac, and Linux, which is a rarity.
Smartdown and Haroopad both are light, easy-to-learn and easy-to-use software. Writers could live within either application for much of their work.