ipLeak - Information that all the sites you visit, as well as their advertisers and any embedded widget, can see and collect about you.
httpStatus - Easily check status codes, response headers, and redirect chains.
WebPageTest - Test a website's performance.
PageSpeed / Insights - Analyzes the content of a web page, then generates suggestions to make that page faster.
serpRobot - Free SERP check, track and monitor your search engine keyword ranking quickly and accurately.
DNSsec-analyzer - A good tool that you can use to check DNSSEC.
ViewDNS.info - Your one source for DNS related tools.
interNet.nl - Test for modern Internet Standards like IPv6, DNSSEC, HTTPS, DMARC, STARTTLS and DANE.
CSR_generator - Advanced CSR, Private Key and Certificate triplet generator.
SSLforFree - Free SSL Certificates & Free Wildcard SSL Certificates in Minutes.
HTTP/3 Check - HTTP/3 Check can query given endpoints for support of both IETF QUIC (HTTP/3) and gQUIC protocols.
Is BGP safe yet - Find out if your ISP implements BGP safely