WordPress.org

Akismet checks your comments against the Akismet Web service to see if they look like spam or not.

By: Matt Mullenweg, Ryan Boren, Andy Skelton, Michael Adams (mdawaffe), and otros.

BuddyPress helps site builders and WordPress developers add community features to their websites, with user profile fields, activity streams, messagin

By: John James Jacoby, Paul Gibbs, Boone Gorges, r-a-y, imath, @mercime, and otros.

The one plugin you need for stats, related posts, search engine optimization, social sharing, protection, backups, speed, and email list management.

By: Automattic, adamkheckler, Andrew Duthie, Alex Kirk, allendav, alternatekev, and otros.

A very fast caching engine for WordPress that produces static html files.

By: Donncha O Caoimh, Automattic, and Brandon Kraft.

bbPress is forum software, made the WordPress way.

By: Matt Mullenweg, John James Jacoby, Jennifer M. Dodd, and Stephen Edgar.

A simple and easy way to test your theme for all the latest WordPress standards and practices. A great theme development tool!

By: Samuel Wood (Otto) and Simon Prosser.