Hey! Thanks for the concise reply. There's a lot of technical stuff I can say about Discourse and such, but because I am the maintainer for NodeBB it is probably in my best interest to keep my mouth shut as we directly compete!
Anyhow, the OrderedCollection stuff is actually all from me. I've been working as part of the Threadiverse working group to bring intercompatible formats to all threadiverse software, which besides Discourse and NodeBB, includes Lemmy, Piefed, and Mbin.
The OrderedCollection enables software (like NodeBB) to quickly backfill entire topics. This is a huge problem on the microblog-side of the fediverse, and is not really a problem on the theadiverse, since there is already strong support for synchronization. However, smaller instances often do run into issues where they can't ever "catch up" on old posts because there's no way to get those posts. (e.g. start following a new community, you can't read any of the old content)
To that end, Lemmy and Piefed have (or soon will) ship code to allow software to backfill using OrderedCollections. They don't use them yet, but they will provide them. It helps software like mine because I will then be able to see entire threads from communities I don't even know about or follow. It's a huge boost to discovery! :smile:
> while Discourse decided to use an OrderedCollection, with the first item being the opening post.
NodeBB also does this, but they're not incompatible per se. You'll see NodeBB topics showing up just fine on Lemmy and Piefed (see activitypub@community.nodebb.org or general), and that's because NodeBB does the extra step of announcing OP and replies, just like Lemmy/Piefed.
Discourse does this too, but because of the inability to find Discourse categories, I don't think it's easy to follow them. Chicken and egg, really.