Ashton Tate made a tree editor called [Framework](http://en.wikipedia.org/wiki/Ashton-Tate#Framework http://en.wikipedia.org/wiki/Ashton-Tate#Framework) which I

Ashton Tate made a tree editor called [Framework](http://en.wikipedia.org/wiki/Ashton-Tate#Framework http://en.wikipedia.org/wiki/Ashton-Tate#Framework) which I used to write my thesis in the late 80s on a DOS machine. I loved it. It had intuitive keystrokes, using the numeric keypad to zoom in (+) and out (-) of the tree with an easy way to collapse the tree branches (enter). Each frame held other frames, or could hold text, a spreadsheet or a database. It wasn’t a DAG (directed acyclic graph) which was frustrating sometimes. I think you could program leaves to link to other leaves, but I wasn’t any good at programming. It had its own programming language FRED. The people who grokked it loved it. I think there is still a [closed source](http://www.framework.com/ http://www.framework.com/) community supporting it, last time I looked. I hope you will use markup with something like YAML or [JSON-LD](http://manu.sporny.org/2014/json-ld-origins-2/ http://manu.sporny.org/2014/json-ld-origins-2/) to store your links.