Zwift.com: it may seem silly to list this first, but this is the place to log in and edit your profile, link up your Strava and other accounts, and more.
Zwift Ride Calendar: want to join in a group ride or race? Here’s the official calendar from ZwiftHQ.
Zwift User Manual: the unofficial guide to Zwift, maintained by James Gill. A huge, living document covering Zwift basics, hardware, levels, and more.
Zwift Riders Facebook Group: an active group of 32,000+ discussing all things Zwift.
Honorable Mention (Helpful Links, but Not Required Reading)
ZwiftPower.com: the place to go for race results (including live results during a race!) Anyone racing on Zwift should register here and link up their Strava account.
Zwift Support Forum: the official community forum of Zwift. Quite active and helpful.
Zwiftcast: listen to each episode while you ride for a big dose of all things Zwift. Includes interviews with Zwift employees plus other movers and shakers in the Zwift community.
What’s on Zwift?: tells you the current Zwift course in your timezone, plus a detailed visual archive of Zwift workouts (built-in workouts plus add-ons). Maintained by Laurens Alblas.
Zwiftalizer: upload your Zwift log and view performance metrics, browse benchmarks of different types of hardware on Zwift, and more.
ZwiftGPS: a helpful app for tracking yourself and anyone you follow live with a map on a second screen (phone, tablet, second monitor, etc). Chase your Strava PRs and more!