HostedScan.com - Online vulnerability scanner for servers, networks, and web applications.
ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
HackerTarget.com - Security Vulnerability Scanning based on Open Source Tools.
Whats My DNS - Instantly check your domain names current IP address and DNS record information against multiple name servers located in different parts of the world.
Intruder - Intruder is a security monitoring platform for internet-facing systems.
NsLookup.io - A simple and powerful tool for querying DNS records