Appsero - Appsero is a killer WordPress Analytics, Licensing & Deployment Tool. Appsero is the perfect companion for WordPress plugin & theme developers.
Textalyzer - Analyze text readability and SEO parameters
Squirrly SEO Focus Pages - Waze for navigating Google Ranking factors
Dareboost: Website Speed Comparison - Check how fast your website is against your competitors
Freemius - Freemius is a suite of solutions for monetization, analytics, and marketing automation for freemium and premium WordPress plugins.
Ubersuggest - Want more traffic? Ubersuggest shows you how to win the game of SEO. Just type in a domain or a keyword to get started.