NapkinBook

NapkinBook is a free, browser-based computational whiteboard for people who make data-driven decisions. Rather than separating diagramming from calculation, it lets users build reasoning chains directly on a canvas: circles hold values, squares perform math operations, and wires connect the pieces together, so a forecast or model becomes a visual, inspectable structure instead of a hidden spreadsheet formula. It's built for forecasters and analysts who want to reason through uncertainty visually — the tool explicitly supports probability modeling alongside plain arithmetic — and who need to bring in outside data via SQL queries or direct data import rather than manual entry. Its creator is described on the site as a 'superforecaster who's worked with Microsoft AI,' though no company name or exact launch date is given. Boards can be created immediately with no signup, and the tool supports live, end-to-end encrypted collaboration and a presentation mode for walking others through a model. Every feature — canvas, math, probability, SQL queries, encryption, and presentation mode — is currently free with no paywall. One limitation: because pricing is not mentioned at all beyond 'free right now,' there's no indication of what, if anything, will eventually be monetized, which makes its long-term availability harder to judge.