Sebastian Fichtner has been working on this app since 2017 but I just ran across it the other day in the Mac App Store. (It's Mac-only.) Design is very similar to Gingko Writer, but seems slicker. Free download, $9.99 for full unlock. Free locked version lets you have 100 items to test it out.

https://www.flowtoolz.com/flowlist/

Dev wrote about it a couple of years ago:

https://www.flowtoolz.com/2018/07/13/how-a-minimalist-productivity-app-changed-my-life.html

Thanks for sharing this find @satis. I am searching for an application similar to Ginko Writer, for longer text writing, and Tree, for outlining. From the explanation, this app works along these lines.

I noticed that the developer has not updated the app in over a year. Umm ...

satis wrote:

Sebastian Fichtner has been working on this app since 2017 but I just
ran across it the other day in the Mac App Store. (It's Mac-only.)
Design is very similar to Gingko Writer, but seems slicker. Free
download, $9.99 for full unlock. Free locked version lets you have 100
items to test it out.

https://www.flowtoolz.com/flowlist/

Dev wrote about it a couple of years ago:

https://www.flowtoolz.com/2018/07/13/how-a-minimalist-productivity-app-changed-my-life.html