Post-Meta-Inspector by Automattic

Adds a table of contents to your WordPress pages based on h3 and h4 tags. Useful for documention-centric sites. Maintained by Automattic on GitHub, where it has earned 45 stars from the community.

Co-Authors Plus add-on pack with profile fields for popular social media services and the ability to allow attributing posts to their Authors when shared using Jetpack. Maintained by Automattic on GitHub, where it has earned 24 stars from the community.

Adding some LOLs to your server-side WordPress A/B testing. Plays nice with Batcache. Maintained by Automattic on GitHub, where it has earned 28 stars from the community.