They are all federated. They do not share the same servers.

You're actually commenting on an article on kbin.social.

Lemmy, kbin, and Mastodon are all different ways to view content posted to "the fediverse" which is basically a bunch of different small servers communicating with each other. They're basically different ways to do view and interact with the same posts, kinda like how you use different services (gmail, etc) for email, and then access that still with different software (browsers, or thunderbird, or what have you). For instance, right now I'm responding to your comment from kbin on my desktop browser.

I'm replying to you from Kbin! Federation is great.

I set up accounts on all three and tried them all out before deciding where I wanted to 'live', it's quite easy, might be worth a go to see what you like.

Everyone already mentioned that they’re federated and running on small servers. From a user perspective, Kbin is most similar to Lemmy as they are both similar to Reddit, but they are different in that they are completely different projects. Kbin seems to have fewer instances running right now, so everything on Kbin is a little more concentrated among the instances that do exist. But since you can access both Lemmy and Kbin from either, I’d stick with whichever one has the interface that you prefer.

Mastodon is similar to Twitter in how it looks and how people use it.

Lemmy is Reddit.
Mastadon is Twitter.

Kbin is a bit of both.

They federate. So imagine using your Reddit account to reply to a tweet. And vice versa.

They don’t share the same servers - they just communicate with each other. Kind of like how I can use Gmail to write to a friend that uses a Yahoo Mail.

@ryknow replying to you on kbin! Federation is really nice!

@tchambers @Jcb2016