This magazine is dedicated to discussions on the federated social networking ecosystem, which includes decentralized and open-source social media platforms. Whether you are a user, developer, or simply interested in the concept of decentralized social media, this is the place for you. Here you can share your knowledge, ask questions, and engage in discussions on topics such as the benefits and challenges of decentralized social media, new and existing federated platforms, and more. From the latest developments and trends to ethical considerations and the future of federated social media, this category covers a wide range of topics related to the Fediverse.
Viewing this video, I found that the ActivityPub is technically a protocol to send/receive social contents in each instance from/to each other.
More interesting thing I found is that it's not only for remaking twitter/facebook/instagram, but also for creating self-controllable novel social internet experiences.
I hope if I can create such collaborative/controllable/secure social tools with it.
You might want to look at https://beehaw.org/post/558211. The Wikipedia article it links too specifically talks about all of the other apps that already exist on the Fediverse.