Are we counting any project implementing ActivityPub as part of the fediverse?
Please note: the list here is no longer updated, and the issue has been closed. From now on this list will be maintained on the wiki of this project: https://gitlab.com/fediverse/fediverse.gitlab.io/wikis/watchlist-for-activitypub-apps
None of these apps ought to be added to the official fediverse.party site until they have been tested with at least one (ideally 2-3) of the AP apps already listed, and can be confirmed to federate successfully. Once it is on the official site, it can be removed from this list, keeping it a list of apps to be watched/ tested.
The SocialWG has a list of projects they hope will implement ActivityPub and links to Issues where it's discussed. Also, there is an implementation report on ActivityPub.rocks. More projects using AP are profiled on We Distribute by Sean Tilley. From these and other sources (see links), it looks like all these apps are either considering, working on, or already rolling out AP support:
Social network, Microblog Apps
microblog.pub - single-user microblog server
microstatus - "Lightweight Mastodon- and GNU social-compatible ActivityPub and OStatus server implementation"
Numa - built on Ethereum blockchain but federates with AP
Smilodon/ Pylodon - web front-end / back-end written in Python
Blog and Publishing Apps
Quit.im this may just be an photo-sharing web client for a GNU social server, rather than a completely separate app, but if so, it will potentially become an AP implementation when the AP plug-in for GS is done.
File, Contacts, and Calendar Syncing Apps
GitPub - a set of extensions to AP for federation between code forges (Git hosting sites like GitLab, Gogs, Gitea etc)
Osada - a bridge server for smoother inter-operation between Zot networks (Hubzilla) and AP networks
Places.pub - AP implementation testing tool?
Pubstrate - experimental AP implementation written in GNU Guile
tags.pub - AP implementation testing tool?