Private, self-hosted software for one household.
These apps run on a private server at home. They are not a public service: there is no sign-up, no shared account, and each app is reachable only from the household's own private network.
Some apps can connect to a service the household already uses, such as a music or media account. Connecting is always optional and always chosen per device. An app then shows that account's own content on that device.