Kbin, Mastodon, Lemmy, and others are all “federated apps” connected to ActivityPub. They are just different UIs to connect to it, so you can see posts and content from one on the others.
Mastodon is a UI inspired by Twitter.
Lemmy is a UI inspired by reddit. It is more stable but less feature rich. You can get native apps just like with reddit, such as Jerboa (similar to rif).
Kbin is a UI inspired by reddit. It is more feature rich and less stable (said to be, anyway).
They are all speaking the same protocol though. So while you can load Mastodon posts in this Lemmy ui they might look … off. Similarly you can load things in Mastodon from kbin etc and they too might seem weird. It’s because they’re not giving the same context you might get viewing that content in the UI it was made for.
These are all still new with Mastodon being the one most widely adopted already. So expect better features and bug fixes to roll out over time. Especially with so much more demand now, I’m guessing many old 3PA devs have already been working out new tricks for ActivityPub.
My highschool days. Wouldn’t change a thing either, except I wouldn’t start smoking cigarettes.