A bit of history. I came up with the term “social linked data” in about 2013, which went on to become Solid. I also around 2011 had the concept of a “Semantic Inbox”, basically an inbox working over HTTP, rather than, SMTP
In the Social Web Working Group both these concepts matured quite a bit, and took on a life of their own, becoming what we see as the solid project today, and inboxes used to power the fediverse
In my head initially I thought that this would all be one thing. So I’m glad someone is working on bringing the two systems together
I see some differences. Solid does identity differently to AP. ie WebID vs Activity Streams Actors. The primary serializations are different. e.g. Turtle vs JSON(-LD). Discovery is different, e.g. webfinger vs follow-your-nose
If I were able to start over, I would have made Solid completely based on JSON-LD, since that is what has gained traction. And have a separate branch of the project for those wanting to use turtle, full rdf, rdf-star, sparql etc. I do like turtle alot, but it’s just that JSON has won that race
What I originally had in mind for Semintic Inbox was a catch all type area for any kind of message. It then was processed and after that, had side effects and notifications. So, if an activity was posted to an inbox, it goes onto a separate timeline area (like in facebook). If a friend request was posted, the user gets a notification and is able to friend back, a payment would have yet another work flow etc. So this was much more an alternative to facebook, whereas alot of the work in the SWWG was to create an alternative to Twitter
The idea of Pods came quite a bit later. We started out with just profiles and authentication. Then we thought it would be nice to store data and apps, creating an organic read-write web. Pods kind of came together with Linked Data Platform which is a way of putting a wrapper around the file system. Files on a file system and http web files were supposed to be parts of an interchangable web space, so you could have a gallery folder on your laptop (or phone), use a desktop app to view it, or use a web type app to view it also. Changes to one space would be reflected in the other (at least in theory)
ActivityPods seems like a cool project. I can imagine a system that enables single-sign-on (eg with PKI) to a number of apps, one of which is web space in the form of a Pod, and where you can interact with other user Pods. I can imagine a useful system where users are able to store photos, videos, html pages, and some JSON data in their own area, and have apps interact with that. Looking forward to seeing what you make!