SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
SEOmator - SEO website analysis & audit tool
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Lumar - (Previously DeepCrawl) Hosted SEO spider to analyze and find problems with websites.
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.