3Proxy tiny free proxy server is really tiny cross-platform freeware
proxy servers set. It includes HTTP proxy with HTTPS and FTP support,
SOCKSv4/SOCKSv4.5/SOCKSv5 proxy (socks), POP3 proxy, SMTP proxy,
AIM/ICQ proxy (icqpr), MSN messenger / Live messenger proxy(msnpr), FTP
proxy, caching DNS proxy, TCP and UDP portmappers.

You can use every proxy as a standalone program (socks, htproxy, tcppm,
udppm, pop3p) or use combined program (3proxy). Combined proxy
additionally supports features like access control, bandwidth limiting,
limiting daily/weekly/monthly traffic amount, proxy chaining, log
rotation, syslog and ODBC logging, etc.

It's created to be small, simple and yet very functional.

3proxy is absolutely free (FreeWare) and open source. It can be used
under terms of GNU/GPL. Starting from 0.6 version BSD-style license is
used and any compatible license (Apache license, GPL, LGPL) may be used
instead.

A user and group "proxy" must exist prior to running this script.
To create them, run as root:
  groupadd -g 396 proxy
  useradd -u 396 -g 396 -s /sbin/nologin -M proxy