Masscan: TCP port scanner, scanning entire Internet in under 5 minutes
Massacan is awesome. One of the usecases is to periodically scan your own servers to see if you have not accidentally opened some new ports in firewalls.<p><a href="https://github.com/bobek/masscan_as_a_service" rel="nofollow">https://github.com/bobek/masscan_as_a_service</a>