MASSCAN: Mass IP port scanner
This is the fastest Internet port scanner. It can scan the entire Internet in under 6 minutes, transmitting 10 million packets per second.
It produces results similar to nmap, the most famous port scanner. Internally, it operates more like scanrand, unicornscan, and ZMap, using asynchronous transmission. The major difference is that it's faster than these other scanners. In addition, it's more flexible, allowing arbitrary address ranges and port ranges.
NOTE: masscan uses a custom TCP/IP stack. Anything other than simple port scans will cause conflict with the local TCP/IP stack. This means you need to either use the -S option to use a separate IP address, or configure your operating system to firewall the ports that masscan uses.
This tool is free, but consider funding it here: 1MASSCANaHUiyTtR3bJ2sLGuMw5kDBaj4T