Libnice is an implementation of the IETF's Interactive Connectivity Establishment (ICE) standard (RFC 5245) and the Session Traversal Utilities for NAT (STUN) standard (RFC 5389). It provides a GLib-based library, libnice and a Glib-free library, libstun as well as GStreamer elements.
Wiki page: http://nice.freedesktop.org/
Reference docs: http://nice.freedesktop.org/libnice/