It's the network part of Torque for use in non Torque engine games.
Quote:The Torque Network Library is a robust, secure, easy to use, cross-platform C++ networking API designed for high performance simulations and games. The network architecture in TNL has powered some of the best internet multiplayer action games to date. Whether you're writing a multiplayer game, developing a complex simulation, or just need a solid foundation for network apps, TNL will meet your needs.
Associate Joseph Euan
(it's used in NCSoft's mmo Auto Assault)
www.opentnl.org/