Squid Proxy - Website Content Acceleration and Distribution. Thousands of web-sites around the Internet use Squid to drastically increase their content delivery. Squid can reduce your server load and improve delivery speeds to clients.
Polipo - A small and fast caching web proxy (a web cache, an HTTP proxy, a proxy server).
Apache Traffic Server - Fast, scalable and extensible HTTP/S 2 and 1.1 compliant caching proxy server.
ExaProxy - ExaProxy is a a high-performance non-caching proxy.
WinGate - WinGate is highly capable web proxy software for Windows: caching, intercepting, forward and reverse proxy with https inspection and SSL offload, SOCKS server, email
Privoxy - Privoxy helps users to protect their privacy.