winfoom

Winfoom is an HTTP(s) proxy server facade that allows applications to authenticate through the following proxies:

NTML or Kerberos HTTP authenticated proxy
SOCKS version 4 or 5, with or without authentication
Proxy Auto Config files - including Mozilla Firefox extension that is not part of original Netscape specification typically used in corporate environments, without having to deal with the actual handshake.

Another kind of proxy made in C is [cntlm|http://cntlm.sourceforge.net/]