I couldn't find much with a quick look. But yes, I have (re)invented this wheel and it seems to work.
There can be as much or little structure as desired and I can output an outline-like file provided
that I ignore circular links. I do this by saying that a parent can have any number of children, but a child can only have one parent, and if I encounter a link that is a second parent for a given node, I simply ignore that link.
Of course, all nodes don't have to be linked to other nodes or to the origin. There can be any amount of standalone structure.
I'll spruce things up a bit and post here in a few days. It's relatively crude but it works.
I could have stayed with VYM, which already outputs org-mode and many others, but I do like Labyrinth's ease of use and particularly speed of use, in addition to the completely free-form placement of nodes. I'm finding it to be a terrific tool for developing ideas for fiction.