The only tool/technique to punch holes through firewalls/NATs where multiple clients & server can be behind separate NATs without any 3rd party involvement. Pwnat is a newly developed technique, exploiting a property of NAT translation tables, with no 3rd party, port forwarding, DMZ, DNS, router admin requirements, STUN/TURN/UPnP/ICE, or spoofing.
Why do you think that https://github.com/sqlmapproject/sqlmap is a good alternative to pwnat