Masscan

This is an Internet-scale port scanner. It can scan the entire Internet in under 5 minutes, transmitting 10 million packets per second, from a single machine.

Its usage (parameters, output) is similar to Nmap, the most famous port scanner. When in doubt, try one of those features -- features that support widespread scanning of many machines are supported, while in-depth scanning of single machines aren't.

Internally, it uses asynchronous transmission, similar to port scanners like scanrand, unicornscan, and ZMap. It's more flexible, allowing arbitrary port and address ranges.