https://github.com/qsun/ParDiff-VPN
开源的MOEVPN – VPN管理销售系统：
http://ichon.me/2012/06/13/moecn-net-opensource.html
https://github.com/chon219/moevpn-ose
https://github.com/bblackham
一个轻量级的VPN解决方案：
http://code.google.com/p/sigmavpn/,
https://code.google.com/archive/p/sigmavpn/wikis/Introduction.wiki
http://github.com/neilalexander/sigmavpn/
https://sourceforge.net/p/sigmavpn/
三个可以用来做防火墙、VPN网关的Linux系统：
http://www.untangle.com/
http://www.clearfoundation.com/
http://alpinelinux.org
