Betatesters.io - The platform connecting mobile developers and beta testers
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.
Betafy - Where startups meet beta users!
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Beta Family - 50,000 testers to test your app
Pulno - SEO Audit and Website Analysis. Pull up your SEO.