@Plastic Paragraph One of the biggest differences is that Mastodon was inspired by pre-X Twitter, and Friendica and Hubzilla were inspired by Facebook.

So the way they handle certain things are different. One of the biggest differences is that Friendica and Hubzilla have threaded conversations, while Mastodon does not. And Mastodon does not support group discussions and forums, while Friendica and Hubzilla both do.

Friendica and Hubzilla are both children of Friendika, which traces its code all the way back to Mistpark (Misty) and Red Matrix. Friendica and Hubzilla both come from the same roots.

Hubzilla, and a project called (streams), have unique features such as nomadic identity and federated single sign on, which is why it comes up in discussions regarding adding those features to ActivityPub. (Friendica might have the ability to turn those on, I am not sure, but I have not seen it in the wild. Whereas in Hubzilla, nomadic identity and federated single sign on are part of the core features set.)