3.1The board

Every project has a board. Open it from Tasks in the desktop app's sidebar, or from the Tasks button on the project page in the dashboard. Both write the same rows, so a card someone drags in the browser moves in the app.

The four columns

Four columns is a deliberate ceiling. A board with twelve states is a board nobody updates, and an out-of-date board is worse than no board because people trust it.

Cards

A card has a number, a title, a description, and an optional assignee. Numbers are per project and increase, so #12 in one project has nothing to do with #12 in another — the same rule commits follow.

The assignee list is exactly the set of people who can open the project: organization owners and admins implicitly, plain members through their project membership. You cannot assign work to somebody who cannot open the board it is on, which sounds obvious and is the kind of thing that silently breaks in most tools.

Ordering

Drag a card and the client tells the server which two cards you dropped it between. The server works out the new rank from that.

The alternative — the client computing a position and sending it — breaks the moment two people drag at once, because each of them computed against a board that was already stale. Describing the drop by its neighbours cannot go wrong that way.