1. Wp mailDocumentation for all the situations where WordPress core sends an email, how and when they happen, and how to filter or disable each one.
2. User SwitchingWordPress plugin that provides instant switching between user accounts.
4. Wp CrontrolWP Crontrol lets you view and control what's happening in the WP-Cron system.
5. Extended Template PartsA library which provides extended functionality to WordPress template parts, including template variables and caching.
6. ExtWP-CLI command which checks the existence of PHP extensions needed to run WordPress.
9. Extended CptsA library which provides extended functionality to WordPress custom post types and taxonomies.