LinkChecker - LinkChecker is a free, GPL licensed website validator.
PH today - A simple realtime view of Product Hunt
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
Product Hunt Digest - A simple open-source product that generates a daily digest of top performing products on Product Hunt directly to your Slack.
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.
500 Makers - An updated list of the Top 500 Makers on Product Hunt