An outliner: ideas under ideas, folded and unfolded, moved around and joined; the same tree a deck or a mind map reads.
A tiny office suite where the link is the document. No accounts. Nothing is saved anywhere unless you choose to keep it on this device. Tiny Little Office needs JavaScript to show a document.
Agents: https://tlo.ericrose.dev/llms.txt says how to make a document as a link; a document goes inside another as a fence named by its app.