I'm happy to announce that my barebones ActivityPub server, implemented in Node.js/Express, is now open source! I intend for it to be a reference implementation for developers who are adding ActivityPub to their own services, but also it is an application server that you can build on if you want.
In other words, t's a few hundred lines of code that lets you create Mastodon-compatible accounts that can accept follow requests and post stuff to their followers.
I actually built a little toy service (that I will also eventually open source) which converts any RSS feed to an ActivityPub actor that you can subscribe to in Mastodon (or any other AP-compatible client).
Play with it if you like! It is SUPER rough and most feeds end up horribly rendered in Mastodon but it's still kinda cool to see it work: https://bots.tinysubversions.com/convert/
Friend Camp features several modifications that were requested by our users.
If you want decent privacy (the info doesn't leave this server), the only way to do that is to set your account to private, only accept friend requests from other friend.camp users, and only ever @ mention other friend.camp users. Once you start talking to people on other servers, all bets are off. Any private message you send to someone on another server could be looked at by the admin of a different server. This is kind of like email: if you are on a private email server, and you send an unencrypted email to a gmail account, congrats, Google now has the content of that email. But also, you do this every day, so, hey. The internet!