I blame all the similar sounding terms and organizations in the fediverse space. It’s actually pretty cool

What SWF is:

In a gesture that’s been a long time coming, Evan Prodromou, co-author of the ActivityPub protocol, has launched The Social Web Foundation. The organization aims to tackle the various headaches and challenges the ActivityPub ecosystem has faced over the last decade of its development. Their mission? A bigger, better Fediverse.

From this article:

the SWF has been working on several interesting projects outside of these stated scopes, and it’s something Evan Prodromou has been bullish about: leveraging the ActivityPub Client-to-Server API. Historically, this piece of the ActivityPub protocol is rarely ever implemented, due to complexity as well as the fact that Mastodon’s own client API has seen widespread adoption.

To really understand the C2S API, we have to go back in time to when the protocol was being developed. The basic concept was that any ActivityPub implementation would effectively act as a generic server, with clients providing unique experiences. Compared to Mastodon’s dedicated API, C2S isn’t explicitly limited to microblogging or statuses. Instead, clients dispatch activities to and from an Actor’s inbox and outbox.

<img alt="" src="https://i0.wp.com/wedistribute.org/wp-content/uploads/2025/08/Board1.png">

Instead of every new social experience in the Fediverse acting as a bespoke server, the C2S API instead lets a wide range of clients interact with an instance. Instances no longer become specific delegates of what activities can or cannot be used. C2S opens the floodgates for any kind of application to hook in to a Fediverse account. Instead of an instance doing all the hard work, clients would handle much of the advanced logic themselves.

Setting aside unique applications for a moment, one of the key killer-features that ActivityPub C2S could offer the Fediverse is a coherent and streamlined login system for any Fediverse account.

It then has some other examples of how this protocol is being used

Yeah, it’s not great. Unfortunately, there’s not a great way to describe this stuff without either leaning into abstract terms, or using oversimplifications.

The short of it is: only half of the ActivityPub protocol really got adopted by most of the Fediverse: the stuff that lets servers talk to each other. The other half would allow for a lot of cool things to be built, with not everything being its own Fediverse server.