[Tools with open protocol issue (not yet implemented), not fully open sourced code, no documentation at all, or alpha state with development inactive for several months - not added for now]
The [SocialWG has a list](https://www.w3.org/wiki/Socialwg/ActivityPub_network) of projects they hope will implement ActivityPub and links to Issues where it's discussed. Also, there is an [implementation report on ActivityPub.rocks](https://activitypub.rocks/implementation-report/). @Mayel from Social.coop is maintaining a [web spreadsheet of AP apps](https://ethercalc.org/fediverse-stacks) and their characteristics. More projects using AP are [profiled on We Distribute](https://medium.com/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:
*Note*: most of these projects include both a back-end and a web client, but this list also includes projects that are only a back-end. Projects that are only a web app, for use with an existing back-end, will go on the client list [here](https://gitlab.com/fediverse/fediverse.gitlab.io/wikis/watchlist-for-client-apps).
*✔ [Friendica](https://friendi.ca/) - [AP support still in beta](https://friendi.ca/2018/11/18/activitypub-support-in-friendica/), due to be included in the December release of stable.
* [microstatus](https://github.com/Arkanosis/microstatus) - Lightweight Mastodon- and GNU Social-compatible ActivityPub and OStatus server implementation
*✔ [Osada](https://macgirvin.com/wiki/mike/Osada/Home) - an AP server that can also act as a bridge for smoother inter-operation between AP networks and Zot networks (Hubzilla)
*✔ [SocialHome](https://git.feneas.org/socialhome/socialhome/issues/522) - currently working on adding AP support to their [Python federation library](https://git.feneas.org/jaywink/federation/issues/7)
*✔ [Huzbilla](https://project.hubzilla.org/) - federated CMS with a range of groupware tools available as plug-ins. Support AP with the [pubcrawl plug-in](https://framagit.org/hubzilla/addons/tree/master/pubcrawl).
* [WordPress](https://gitlab.com/fediverse/fediverse.gitlab.io/wikis/Wordpress-integration-with-Fediverse) - an [AP plug-in](https://wordpress.org/plugins/activitypub/) by @pfefferle@mastodon.social, that allows users on AP apps to follow WP blogs, was recently updated. See also [Pterotype](https://getpterotype.com/), which @pfefferle says is currently more feature complete. WordPress is now [listed as a project on the-federation.info](https://the-federation.info/wordpress).
*✔ [FunkWhale](https://medium.com/we-distribute/funkwhale-an-open-source-grooveshark-alternative-begins-activitypub-implementation-cbc10a412b20) - music streaming
* [Quit.im](https://quit.im) - this is a photo-sharing web client for a GNU social server, rather than a completely separate app, so it will become an AP implementation when the AP plug-in for GS is done.
* [Calendar-social](https://gitea.polonkai.eu/gergely/calendar-social/issues/122) - no specific mention of ActivityPub on the repo but rumour on the fediverse is that it will be an AP app. I will post a question on their issue tracker.
*✔ [CommonsPub](https://gitlab.com/OpenCoop/CommonsPub) - a fork of Pleroma intended to provide a UX that supports economic transactions and coordination
*✔ [ForgeFed](https://github.com/forgefed/forgefed/) (formerly GitPub) - a set of extensions to AP for federation between code forges (Git hosting sites like GitLab, Gogs, Gitea etc)
* [GitLab](https://gitlab.com/gitlab-org/gitlab-ce/issues/4013) (see also: https://gitlab.com/gitlab-org/gitlab-ce/issues/30991 and https://gitlab.com/gitlab-org/gitlab-ce/issues/44486)
* [Pleroma relay](https://git.pleroma.social/pleroma/relay) (listed in the-federation.info and fediverse.network as ActivityRelay) - "Generic [LitePub](https://github.com/litepub/litepub) relay (works with all LitePub consumers and Mastodon)"
A place to list rumoured projects for further research, apps whose developers have expressed interest in implementing AP, and vapourware projects that have been planned but no usable code has been written yet.
* [Communecter](https://github.com/pixelhumain/) - already supports ActivityStreams, [plans to implement the rest of AP](https://www.loomio.org/d/Y8kHSzPE/activitypub-as-a-decentralized-oae-infrastructure-/3). Codebase is currently being [refactored into a set of smaller components](https://www.loomio.org/d/Y8kHSzPE/activitypub-as-a-decentralized-oae-infrastructure-/19).
*✔[GangGo](https://git.feneas.org/groups/ganggo/-/issues?scope=all&utf8=%E2%9C%93&state=opened&search=activitypub) - may be starting to implement AP, information is scarce. I have [opened an issue](https://git.feneas.org/ganggo/federation/issues/17) to ask.
* [Indienet](https://source.ind.ie/indienet) - [homepage](https://indienet.info/) - projects goals seem similar to the federated homepages of the IndieWeb, but federated using AP.
* [Spritely](https://gitlab.com/spritely/spritely) - a new federated media-streaming server in Ratchet, planned by Chris Webber of MediaGoblin fame
#### Dead Projects
Listed on this watchlist just in case anyone doesn't realize they're dead, and thinks we just didn't know about them. Also in case a project is orphaned, then reactivated by a new developer.
* [CloutStream](https://web.archive.org/web/20180808152307/http://cloutstream.com/) - proposed as a federated replacement for LinkedIn. Original Mastodon.social account appears to have been removed ([copy on Pinafore]( https://pinafore.social/accounts/25168)), all the links projects tools appear to be down.
* [Fontina](https://github.com/beta-phenylethylamine/fontina) - proposed as a photo-sharing social media network. GH repo has gone read-only, and now says "dead project".
* [Numa](https://github.com/numaverse/numaverse-gateway/issues/3) - built on Ethereum blockchain but intends to federate with AP. No commits since April 2018. No reply on issue about AP compatibility testing from May 8.
