Packagist is the main Composer repository. It aggregates public PHP packages installable with Composer.
Allows error logging as a post type.
Provides numerous performance tools and functionalities to assist in developing high performance WordPress themes
Adds several Theme Customizer controls
Adds ability to easily cache widget output for better performance.
Allows cache items to be tied to a single validation key
Creates a modal window for media selection in WordPress 3.5+