How to make PC behind firewall become a socks proxy server for internet clients?

[nifflin]

It's known that, in internet, a proxy server should have a public ip and port, then, clients in internet could access the web with this proxy.
But TOR changed our perception, PC behind firewall should also become a proxy server for internet clients.

It's a pity that TOR is blocked or censored in many coutries, and it's slow.I don't need the security of TOR, What i need is to make my PCs behind firewall to be socks proxy servers for internet clients (without router port mapping...).

Does there exists some open source solutions for my need? Thanks a lot!