What is ActivityPub?
ActivityPub is a decentralized social networking protocol that powers Mastodon, Pleroma, and other social networks. Users of ActivityPub-compliant apps can like, share, and follow users and content on other ActivityPub-compliant services; for example, a Mastodon user could share or reply to a post from a Pleroma user. This network of connected social services is called the Fediverse.
What is Pterotype?
Pterotype connects your blog to the Fediverse by giving it an ActivityPub feed. This means that users of Mastodon, Pleroma, and other Fediverse applications can discover your blog from within that service and share your posts across the Fediverse.