Reproof
I've always wanted a writing app built around experimentation, where you could write multiple takes on a paragraph then swap them in and out to see how each sounds in context. That, and I wanted a writing app that treated both Markdown and Rich Text as first class citizens, with side-by-side documents for notes alongside a draft, full keyboard control, and more. And so I built it: https://reproof.app/ It's taken forever (never reinvent the text editor, they say, and they're right) but it's finally at the point where a handful of us are using it for daily writing, and it's just about ready to launch.