Lemmy Apps

Long post/response incoming so apologies in advance (tl;dr is near the bottom in bold).

You are correct; Think of it like emails. Particularly the @outlook vs @gmail vs @yahoo, except with @lemmy and @kbin.

You can have a JohnJacob372@lemmy and a JohnJacob372@kbin and it be two separate people with the same username, but different "instances" just like email addresses.

The point is though, that everything that's part of the "fediverse" (Lemmy and Kbin are two of the biggest but there also exist others like Fedia.io) is connected in a way that if you're on one, you can see posts from the others. Ex: If JohnJacob372@lemmy posts an article on Lemmy, it'll show up on your kbin feed/frontpage and you can comment on it along with the lemmy folks.

You can tell where it originated from because it'll say next to the username and magazine (magazine is what you might call a subreddit, but again, you can have same named subs as well, one on Kbin and one on Lemmy). Ex: [email protected] 2 hours ago to [email protected].

If you don't see the @ part after the name or magazine, it means it was posted by someone on your same instance (otherwise it would be "redundant" to say "JohnJacob372 from your neighborhood on Main Street just posted a flyer in your neighborhood on Main Street" when you can just say "JohnJacob372 posted a flyer on Main Street").

So recap (tl;dr):
Instance = Platform (like Lemmy and Kbin)
Magazine = Subreddit
Username@InstanceA can post on Subreddit@InstanceA, and Anyone@InstanceA can read posts on AnySubreddit@AnyInstance (so long as the instance is "federated" i.e. part of the Fediverse Network like Lemmy and Kbin).

Hopefully that helps. You can stop here if you don't want to be confused more, but I will say this:

It may be beneficial, at least in the early days, to have an account on different instances. Mainly because each instance is ran on personal servers by individuals which can have a lot of problems, especially when they are overloaded (like during large migrations from Reddit to here). Having an account on another Instance is like having another account on another Server that can still access the same posts, but because it's a different server, it might be up and running while the other is down for maintenance.

Ideally, apps will eventually be able to switch between instances automatically, but for now, it's easier for app developers to focus on one instance at a time which is why you see different apps for Lemmy and Kbin. This is where my own understanding could be fuzzy because afaik you should still be able to access posts from both (all) instances, it's just that you would need to have an account on the instance/server that app is based on. So an app for Lemmy means you would need to have a Lemmy account, but you should still be able to access/read content posted on Kbin. I think. I could be wrong and you can only see/access content on Lemmy if that's the case. But even then, it won't be forever. These things take time but it's definitely an achievable goal.