I'd just like to interject for a moment. What you're refering to as Lemmy, is in fact, a part of the Fediverse...

I'd just like to interject for a moment. What you're refering to as Lemmy, is in fact, a part of the Fediverse, or as I've recently taken to calling it, the Threadiverse. Lemmy is not a protocol unto itself, but rather another free software server of a fully interconnected Fediverse, made useful by the ActivityPub protocol as defined by the World Wide Web Consortium.

Many computer users interact with a version of ActivityPub every day, without realizing it. Through a peculiar turn of events, the version of ActivityPub which is widely used today is often called Mastodon, or Lemmy, and many of its users are not aware that it is basically the ActivityPub system, developed by several independent projects such as Mastodon, Lemmy or Kbin.

There really is a Lemmy, and these people are using it, but it is just a part of the Fediverse they use. Lemmy is the implementation: the program in the server that allocates the messages to the other servers that run in the Fediverse. The implementation is an essential part of the network, but isolated by itself; it can only interact in the context of a complete federated network. Lemmy is normally used in combination with either instances of itself, or of similar projects of the Threadiverse such as Kbin: the whole network is basically ActivityPub with Lemmy as a node. All the so-called Lemmy servers are really nodes of the Fediverse!