FoldingText 3 development is in flux. Big picture is I built it together with @mutahhir. He was working on FoldingText 2 updates for a while, but sales were not great. He’s then made a few starts on ideas to change things for FoldingText 3, but those ideas are still in flux. We can’t really promise that there will be further FoldingText releases (though we still hold out some secret hopes), that’s why the current version has been made free until we can decide if there’s a future for it.
Yes, this is one of the great things about FoldingText, the underlying document is just plain text. You should be able to open and view in any text editor, for example TextEdit on macOS can open FoldingText files. (you will see text, but not see FoldingText’s special features). You can also open FoldingText documents in one of the many “Markdown” editors on macOS… still won’t get all FoldingText features, but the header/list type formatting will be highlighted.
TaskPaper 3 should work well on Mojave, unlike FoldingText I’m actually updating TaskPaper. See: