Connect a source
Your store, your books, your database, your spreadsheets. Pasted once, synced on their own.
Every source works the same way: you paste one thing, the first pull of history lands while you watch (however big, and always free), and after that it syncs on its own. Hourly on Free, as often as every five minutes on Paid. When a sync breaks, a card shows up in your inbox saying what broke and, usually, the fix.
Shopify
Ten minutes. In your Shopify admin, allow custom apps, create one called Overscore with the four read-only scopes (orders, all orders, customers, products), install it, and copy the token that starts with shpat_. Paste it with your shop handle. Orders, customers and products come in with full history.
Stripe
Five minutes. In the Stripe dashboard make a restricted key with every resource set to Read and nothing on Write; it starts with rk_live_. Paste it. Charges, customers, subscriptions, invoices and refunds come in, and changes update within the hour through Stripe's event feed.
QuickBooks Online
Twenty minutes the first time, because Intuit makes you create a developer app and sign in once. The in-app guide walks through it click by click. You end up with four values to paste; after that it syncs invoices, payments, customers, vendors and the chart of accounts.
Your own database
Postgres, wherever it runs. Two ways: live attaches it read-only and queries run against it in place (point it at a read replica, never the primary), or copy snapshots the tables you name every hour, which is right when the database is busy or you want history. Either way you make a read-only login first; the guide has the five lines of SQL.
Spreadsheets and files
Drop a CSV, Excel, JSON or Parquet file on the Sources screen. It becomes a table. Drop a new version and it replaces the old one, with every old version still reachable. A public Google Sheet link re-pulls on a schedule you set.
Webhooks and other apps
Any app that can post JSON can post to a table. Make an address on the Sources screen, paste it into the other app, and rows land as they happen. Stripe and other signed senders are checked, and fakes are kept in a log with the reason. Slack channels can be kept the same way.