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.
Follow friends and discover new ones. Publish anything you want: links, pictures, text, video. This server is run by the main developers of the Mastodon project. Everyone is welcome as long as you follow our code of conduct!