Virusdie - All-in-One cloud-based, simple, powerful and gorgeous website security tools built for everyone.
Website Grader - Grade your website's strengths and weaknesses in seconds.
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.
PageSpeed Ninja - One-click page speed boost for WordPress
Chaos Toolkit - A chaos engineering toolkit to help you build confidence in your software system
WebSite Auditor - The techie's SEO spider: find site issues other tools miss