ActivityPub support was introduced in version 1.6, with the intention of making it Mastodon's primary communication protocol.
- instance: a brief definition
- people: a directory
- tech: details about how it works
- usage: user guides
- admin: administration guides
- The Mastodon Wiki (not sure who runs this)
- Mastodon instances: an automated list of all known Mastodon instances, with technical ratings
- Instance Recommendations (
viavia) "Some general suggestions for whitelisting, blocking and/or silencing instances"
- Mastodon Apps: official list of apps available or in progress
- kitty.town (home):
- First Toot: look up the first message posted on any public instance
- 2018-01-22 The Mastodon In The Room (via) by Sadiq
- 2017-11-30 Update and retrospective
- 2017-10-19 Mastodon 2.0: The Big Emoji Update by Eugen Rochko
- 2017-08-01 M for Mastodon by Eugen Rochko
- 2017-07-07 Connection: Meeting a Mastodon for Lunch (IRL) (toot)
- 2017-06-15 I have to say that it's slightly irritating when new users (wrongly) imply that...: some myths about Mastodon
- 2017-05-07 One Week of Mastodon
- 2017-04-23 Mourning Mastodon (share and)
- 2017-04-05 Mastodon is dead in the water
- 2017-04-04 Mastodon Is Like Twitter Without Nazis, So Why Are We Not Using It?
Managed hosting for Mastodon instances:
- run by CobaltVelvet (also admin of octodon.social)
- masto.host: hosting for Mastodon instances; they provide maintenance
- run by email@example.com
- Nerdpanel: reads your Mastodon posts and lets you search them; does not store anything on a server
- Mastodon.py: Python wrapper for Mastodon API
- Mastodon Tools: PHP code that interfaces with Mastodon in various ways
- Halcyon: a PHP client for Mastodon, and related stuff
- SupportBot: "A framework for making social media bots for multiple networks" written in Python
- Mastodon Bridge: cross-correlates your Twitter and Mastodon account, and shows commonality (only for users who have used the same tool)
- https://github.com/tootsuite/mastodon-bridge - source code (Ruby); good example of how to allow an app to access Mastodon, which effectively includes authentication
- mastodon-backup: "Archive your statuses, favorites and media using the Mastodon API (i.e. login required)"
- a way to set up auto-replies filtered by instance 
- where X is a set of users chosen by user Y, collect stats about users who follow them or are followed by them (e.g. list users who follow a lot of them or are followed by a lot of them, possibly for autoblocking) and make those stats available to user Y.
- 2017-06-26 Moderation hotfix - mst3k.interlinked.me, coales.co (archive): note about a reverted block