We have Lemmy.world, Lemmy.ml, beehaw.org, I think even yiffit.net. If I log in using wefwef it asks me where I want to login. And when I make a new account using another instance, it says ”… Lemmy is federated, so you can interact with everything on lemmy.ml even if you’re registered on a different instance.“ So if I’m registered on lemmy.world, how can I interact with lemmy.ml?
It’s pretty seamless. Like I can switch from instance to instance, and all is exactly the same (minus instance specific admin stickies) across everything, for the most part. It’s going to depend on the white/blacklist of each instance, but so far I have not found too much that was blocked off on one that I could access from another.