CCProxy - Want to share Internet connection? Get every computer online through a single Internet connection?
Apache Traffic Server - Fast, scalable and extensible HTTP/S 2 and 1.1 compliant caching proxy server.
3proxy - 3proxy freeware proxy server for Windows and Unix. HTTP, SOCKS, FTP, POP3
FreeProxy - Feature summary from website:* Internet connection sharing with demand dialling
Varnish - High-performance HTTP accelerator
gate.js - gate - Performance & scalable I/O forward & reverse HTTP proxy based on node.