Rotas, dues, votes and sign-ups can run on an app your community owns.
Most groups live on someone else's platform. The chat app decides who sees the message, the payment app decides the fee, and the spreadsheet lives in one person's account.
A community can own its tools. Dues and pots, giving that everyone can see is used well, events, votes and rotas can each run on an app with the group's name on it, deployed to a wallet the group controls.
Each app comes with an owner kit that explains how to run it, so it does not depend on one person staying.