I think you can follow Peertube channels and write comments but not post videos. And you can't access Mastodon nor Pixelfed.

Lemmy is centered on the concept of ActivityPub groups. While Mastodon etc are about individuals, they don't use that concept (with their toots) and since following accounts isn't implemented in Lemmy, there is no way to properly interact.

Though there are other software projects. MBin combines both. And Piefed wants to get there, eventually. They already hook into a few more things, but Mastodon or Pixelfed accounts currently aren't properly supported either. But Mastodon people can write replies to our posts.

It's a bit complicated. And I think ActivityPub is fairly low level and broad (I think). So it's really down to the individual implementation and whether two projects agree to do something in a compatible way. And write code for the specifics of some content types.

Like others have said, you can follow accounts from those servers. If they present themselves as group actors, as Lemmy (unlike Mbin for example) doesn't allow following non-group actors.

You can't however just go to their website and log in with your Lemmy account. ActivityPub doesn't have a built-in mechanism for this, but some platforms like Mastodon iirc have a solution and there have been efforts made to standardize something. But there's nothing supported by the Lemmy side of the fediverse yet afaik.

If you want to subscribe to a group actor from Lemmy but can't find them, try searching for the full URL from its home instance. That should tell it to go and fetch the actor. If you want a Lemmy-like experinece but also the ability to follow non-group actors, switch to Mbin. Same applies there, if you can't find an actor on your instance, search for their full URL on the search page and it should fetch them from their home server.

Quick clarification, because I can't tell from your words if you're confused about the concept of federation or not 😅

If by "join" other servers you mean use their site as if logged in, or like you have an account there, then that is not federation. That's single-sign-on (SSO) and is not a feature of the fediverse (Mastodon, Lemmy, Peertube, etc). That would be like the "login with Facebook" or Google buttons around, where by having this account on site A, you can instantly signup on site B without making a new password or anything. That's not how federation works.

Federation is like email. I can have an email with GMail, you can have one with Proton, and someone else can have Yahoo, and I can send an email to you anyway. It doesn't mean I can "join" Proton with my GMail account, it doesn't mean I have a Yahoo account, it means I don't need a Yahoo account to communicate with Yahoo users.

But, if by "join" you meant "join a community" as in subscribe to updates from a group on another server, then most other people's answers apply. I wouldn't call that "joining a server", though, because servers host many communities and you're not joining all of them.

Joining a community works like joining a mailing list. Activity Pub allows accounts on different servers to communicate without an account on their own server, so my account would send a message to your account saying "I'd like to subscribe to this community, send me a message whenever something happens on it", and then the other server says "okay, will do", and then after that will periodically send my server messages saying "hey, here's that update you asked for". And when I comment, like right now, it's like an email being sent from my server to yours, and then your server puts it into the history.

This allows my server to present the community from your server to me, without me having account on your server. Without me having to "join" your server, I'd say.

With lemmy account you can only join "groups", so other Lemmy communities, or equivalent piefed or nodebb.

With a Mastodon account you can also join groups (Lemmy etc), but you can also follow single accounts from any mastodon, pixelfed, peertube etc instance.

Why then having a Lemmy account? The interface, how you see the posts, depends on the software. Lemmy is reddit-like, mastodon is twitter-like etc

If you want to upload your video to a peertube instance, then you need an account on that instance

On Lemmy I can join other servers without having to recreate an account.

Not sure what you mean by "join". You can participate on other Peertube servers, just as you can participate on other Lemmy servers. If you sign up on another server, you will need another account. But currently Lemmy does not support following PeerTube channels. PieFed does.

As for Mastodon, The threadiverse (Lemmy + Piefed, etc) is not intended to follow individuals so it does not have that capability. However if a microblog user replies to a threadiverse user, you will be able to see and interact with that as well.

Hope that helps. Happy to hop on a call or something with you to share what I've learned for your presentation.

In my opinion this is the biggest shortcoming of the ActivityHub ecosystem. That's not to say it should have been solved by now, since I don't know how to decentralize authentication safely. And after using it for a while I'm not sure I want a single account.

But it is a challenge facing newcomers and those trying to recruit them. This group of services is already tough to explain sometimes, and telling them it all interconnects just muddies the waters when you have to explain that it's not the way they expect.

@Snoopy@feddit.fr, I think it works for Piefed?

No. For each Mastodon, Lemmy, or Peertube server you want to join, you need a separate account on the server.