Parent/child Single sections I'm trying to create parent/child Single sections without using Structures.  So in other words, create a Single section and assign it a parent Single section.  Is this possible?
Ignoring the obvious "use a Structure" answer, I suppose you could fake a "hierarchy" by placing a child and parent entry field on each of your Single sections and manually assigning entries as relationships.

Then your Twig template could would just be checking those fields and building the family tree based on the relationships.