[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)
* [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.
*✔ [NextCloud](https://help.nextcloud.com/t/activitypub-the-new-standard-for-decentralized-networks/26381) - seem to be only using AP for internal federation?
*✔ [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)
* [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).
* [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.