In this very thread I have seen responses from people who are using Pleroma or Misskey or Calckey or Friendica as their instance software. This very thread shows exactly how this is a bigger network than just Mastodon.
You can use a Mastodon app and connect to a Mastodon instance and never even know that person you're talking with is using, say, Fedilab with a Pleroma instance.
Recognizing that is, I feel, useful, as it broadens our imagination about what's possible. :blob_derpy: