I moved from mind maps (I used and liked FreeMind) to indented outlines in plain text files when I realized I wasn't really losing anything to map the nodes to headings and the edges to sub-headings. I can capture the same relationships, keep it synced to everywhere via cloud storage, and I don't need special software beyond a text editor to look at or edit it.
Now I just need to learn how to go back through them.
Now I just need to learn how to go back through them.