This is an OCaml library for handling TUN/TAP devices. TUN refers to layer 3 virtual interfaces whereas TAP refers to layer 2 Ethernet ones.
See http://en.wikipedia.org/wiki/TUN/TAP for more information.
Linux, FreeBSD, OpenBSD and MacOS X should all be supported. You will need to install the third-party http://tuntaposx.sourceforge.net/ on OSX before using this library.