Stone is a TCP/IP packet repeater in the application layer.  It
repeats TCP and UDP packets from inside to outside of a firewall, or
from outside to inside.

Stone has following features:

1.  Simple.
        Stone's source code is only 3000 lines long (written in C
        language), so you can minimize the risk of security
        holes.

2.  Stone supports SSL.
        Using OpenSSL (http://www.openssl.org/), stone can
        encrypt/decrypt packets.

3.  Stone is a http proxy.
        Stone can also be a tiny http proxy.

4.  POP -> APOP conversion.
        With stone and a mailer that does not support APOP, you can
        access to an APOP server.