6bone
The 6bone was a testbed for Internet Protocol version 6; it was an outgrowth of the IETF IPng project that created the IPv6 protocols intended to eventually replace the current Internet network layer protocols known as IPv4. The 6bone was started outside the official IETF process at the March 1996 IETF meetings, and became a worldwide informal collaborative project, with eventual oversight from the "NGtrans" (IPv6 Transition) Working Group of the IETF.
Read more about 6bone.