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.
UI Movement - The best UI design inspiration, daily
Fast Link Checker - An advanced tool to find broken links on web sites.
Design Hunt - Curated design inspiration for everyone
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
UI Jar - Hand-picked design inspiration for your real life projects