Wikipedia
VTun
VTun is a networking application which can set up Virtual Tunnels over TCP/IP networks. It supports Internet Protocol (IP), Point-to-Point Protocol (PPP) and Serial Line Internet Protocol (SLIP) protocols. It exists as the reference implementation of the Tun/Tap user-space tunnel driver which was included in the Linux kernel as of version 2.4, also originally developed by Maxim Krasnyansky. Bishop Clark is the current maintainer.