WP Rocket - WP Rocket offers a caching plugin for Wordpress.
KeywordTool.io - KeywordTool.io is the best FREE alternative to Google Keyword Planner and Ubersuggest. It uses Google's autocomplete feature to get over 750+ long-tail keywords for any given query.
Yoast - Yoast offers plugins to improve SEO and optimize web sites and blogs.
Google Trends - Explore Google trending search topics with Google Trends.
Wordfence - Comprehensive security plugin for WordPress.
Keywords Everywhere - Free browser add-on for keyword volume, CPC & competition