SISTRIX - SISTRIX toolbox is an SEO tool for professionals helping reputable companies to constantly improve their websites.
Website Grader - Grade your website's strengths and weaknesses in seconds.
Page Weight - Find and fix heavy images on your website
PageSpeed Ninja - One-click page speed boost for WordPress
Checkbot - Checkbot will boost the SEO, speed and security of your site by checking you're following 50+ web best practices. Browser extension with free and paid plans.
Ryte - Ryte is a web-based software invented for technical optimization for search engines and improvement of websites.