pfSense - pfSense is a free and open source firewall and router that also features unified threat management, load balancing, multi WAN, and more
Polipo - A small and fast caching web proxy (a web cache, an HTTP proxy, a proxy server).
Zentyal - Linux directory, domain, mail, gateway and infrastructure server for SMBs.
Privoxy - Privoxy helps users to protect their privacy.
NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
ExaProxy - ExaProxy is a a high-performance non-caching proxy.