Most productivity setups are five apps in a trench coat. Tasks in one, notes in another, money in a spreadsheet, habits in a phone app, and the household coordinated over text messages. Each one is good at its job and completely incurious about the other four.
The Margin is one system of record for all of it. Boards, a weekly planner, notes, habits, expenses, focus sessions, whiteboards, and a family layer for the people you share a life with.
The pieces
Workspaces are the outermost container. Everything you create belongs to one. Most people have a personal workspace and, if they share a household, a family one. You can belong to several, and you switch between them from the sidebar.
Modules are the surfaces inside a workspace: Boards, Planner, Today, Notes, Habits, Expenses, Focus, Whiteboards, Journal, Checklists. Each has its own colour in the sidebar so you can tell where you are without reading.
The Mind is what makes them one thing rather than ten. It reads across everything you have written and keeps a memory of the people, projects and commitments that keep coming up. See The Mind.
Margin AI is the assistant. It uses the same tools an external agent would, so anything it can do, you can do, and anything you can do, it can do. See Margin AI.
Two kinds of data, and why you can feel the difference
Your own material (boards, cards, notes, habits, expenses, whiteboards) lives in a real database on your device. You can edit it on a plane. It syncs when you reconnect.
Your account material is different: which plan you are on, who is a member of your workspace, what role they have. That lives on the server and only on the server. A device that could edit its own subscription tier would not be a business, and a device that could promote itself to owner would make permissions decorative.
The practical consequence: notes and boards work offline, billing and member management do not. That is a design decision rather than a gap. See Working offline.
What it is not
It is not a team project tool that happens to allow personal use. The household is the first-class case, and the team workspace is built on the same sharing model rather than the other way round.
It is also not finished. Where a page here describes a limit rather than a feature, it says so plainly.