Yoast - Yoast offers plugins to improve SEO and optimize web sites and blogs.
Jackmail - A newsletter plugin for Wordpress.
Wordfence - Comprehensive security plugin for WordPress.
Event Espresso - Event Espresso offers event registration and ticketing management plugin for WordPress.
WP Rocket - WP Rocket offers a caching plugin for Wordpress.
Gravity Forms - Gravity Forms is one of the best and easiest contact form plugins to create modern forms for websites powered by widely-used WordPress.