I’d recommend installing a Pleroma server. It speaks ActivityPub and you can use any of the nice Mastodon apps with it. I've run a Mastodon server for the last 9 years, and wouldn't recommend Pleroma over it for a large many-user instance, but it's relatively tiny and lightweight for a personal server. You can configure it not to talk to the rest of the Fediverse so that it remains your friendly, isolated silo.