Best and most general option that I know of is Org mode (Emacs). But regardless, I'm glad more people are picking up on the power of hierarchical text editing (

Best and most general option that I know of is Org mode (Emacs). But regardless, I'm glad more people are picking up on the power of hierarchical text editing (and interfaces more friendly to non-programmers are a reasonably good thing). But if you really want to go all the way, and get arbitrary directed graphs of text content, check out org-brain.