crt.sh
Public certificate transparency search for issued certificates and names they cover.
Have I Been Pwned
Find public records of known data breaches.
ICANN Lookup
Public domain registration lookup using ICANN registration data.
ipinfo.io
IP address location and network information.
National Vulnerability Database
The U.S. National Vulnerability Database provides publicly reported security vulnerabilities, with recent product matches and CVE details, including CISA catalog status and affected versions when reported.
SSL Labs
Qualys SSL Labs tests the security of public HTTPS servers.