Miro

Promptfree, for everyone, and the only version there is

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Do not build this. Multiplayer on a canvas is years of work, and the templates are most of why it gets opened.

Hit testing, selection, snapping, undo across simultaneous edits, and sixty frames a second with thousands of objects — that is the engine. On top of it sits a library of workshop formats somebody designed, which is what makes a facilitator choose it over a wall of paper.

WHEN TO KEEP PAYING
- Workshops with people who are not all in one room
- Anything where several people edit at once and it must feel immediate

WHAT TO USE INSTEAD, FREE
- **Excalidraw**, which is open source, self-hostable, and genuinely pleasant. It covers diagrams and sketching outright
- **tldraw**, if you want a canvas inside your own product — and note that shipping it commercially without branding is a licence, which is covered elsewhere in this catalogue
- A shared document, for a surprising share of what boards are used for. Much of what happens on a whiteboard is a list that grew legs

WHAT YOU CAN BUILD, AND SHOULD
**A narrow diagram editor with fixed shapes**, if the requirement is specific: labelled boxes and connectors, a floor plan on a grid, a node graph for your own domain. That is a week rather than a year, and the entry under tldraw sets out the shape

If you do:
- Build the undo stack before the second shape type exists. Retrofitting undo is far harder than building it in
- Z-order as fractional indices, not integers — integer ordering renumbers on every move and floats run out of precision
- Arrows that stay attached when their endpoints move, which means bindings rather than coordinates
- Use an existing conflict-free replicated data type library if more than one person edits. Writing one is a research project and getting it subtly wrong loses people's work

AND THE THING WORTH MORE THAN THE BOARD
Export whatever you have. A board full of a year of workshops, readable only inside one product, is a year you do not own. Export to the open format on a schedule, into a directory you back up, and check that what comes out is still legible.

THE ONE-LINE VERSION
Use Excalidraw for diagrams. Buy the board for workshops, and export it on a schedule.