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.