To be more precise, ActivityPub is pretty much just a JSON/HTTP version of email. There's a few fancy things to have stuff like user profiles and stuff to make

To be more precise, ActivityPub is pretty much just a JSON/HTTP version of email. There's a few fancy things to have stuff like user profiles and stuff to make it "look nice", but if you look "under the hood", the data structures you find ends up and the methods of communication end up looking more or less like a modernized version of email. --- Mastodon is a sub-implementation of AP that follows some of the components and then weirdly tweaks some of them in weird ways (because Mastodons internal representation doesn't actually match up with these data structures and Gargron wanted some features like Content Warnings without bothering with the entire process of protocol modifications, so he ended up cannibalizing a different field for it, resulting in an implementation that... mostly results in people yelling at each other for not using CWs "appropriately"), resulting in strange compatibility issues when writing your own AP instance. Most AP instances typically end up trying to then match Mastodons weird implementation (basically look at the social feed of any AP implementer for long enough and you'll find complaints about how Mastodon doesn't follow the spec), simply because of Mastodons excessive popularity.