The GLib ICE implementation
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.
ICE is useful for applications that want to establish peer-to-peer UDP data streams. It automates the process of traversing NATs and provides security against some attacks. It also allows applications to create reliable streams using a TCP over UDP layer.
Existing standards that use ICE include Session Initiation Protocol (SIP) and XMPP Jingle.
Mailing list: http://lists.freedesktop.org/mailman/listinfo/nice
Farstream is a complete streaming implementation, build for peer-to-peer audio and video, that uses libnice.