Mx ToolBox - https://mxtoolbox.com/blacklists.aspx
BPG Hurrican electric - https://bgp.he.net/
Qualys SSL test - https://www.ssllabs.com/ssltest/
Gordon - https://gordon.mhg.ovh/
PulseDive - https://pulsedive.com/
Whois search - https://whois.domaintools.com/
VirusToal - https://www.virustotal.com/gui/home/search
URLScan - https://urlscan.io/
DNS Dumpster - https://dnsdumpster.com
Wappalyzer - https://www.wappalyzer.com
Builtwith - https://builtwith.com/
Exploit-DB - https://www.exploit-db.com