So far I have understood it.
I meant the question in the most practical way: how can I make different software in the Fediverse interact, and which ones can interact with each other?
For example, since it is possible to follow a Lemmy community on Mastodon is it also possible to do the reverse and follow a Mastodon user here on Lemmy? Or is it possible to follow a Peertube channel here on Lemmy?