A spreadsheet with formulas, named cells and charts; three columns to start, more as you need them.
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.