@wion OStatus and its !groups is an example of how it worked in earlier iterations of the fediverse. #Prismo, #Anancus, #Lemmy, and #Mooncake are all projects working on federated #Reddit-a-likes using #ActivityPub, so compatible with Masto et al. See 'link-sharing and forum apps' on this watchlist for updates:
https://gitlab.com/fediverse/fediverse.gitlab.io/wikis/watchlist-for-activitypub-apps
I don't know much about #Mobilizon yet but my understanding is that it's more a replacement for FB events, #MeetUp.com, etc
@Stoori