HackerOne - HackerOne provides a platform designed to streamline vulnerability coordination and bug bounty program by enlisting hackers.
Domain Details - Displays Server Type, Headers, IP Address, Location Flag, and links to Whois Reports.
SafeHats - Safehats is providing bug bounty and vulnerability disclosure services to enterprises.
ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
YesWeHack - Global Bug Bounty & Vulnerability Management Platform
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.