December Lab Report #11 of 12 - The Future, Embracing The Past news - Zircon Engine - a "DarkPlaces Mark V" project mod for Quake
Zircon now supports protocol 666 and 999, giving it the ability to play demos recorded in Quakespasm, connect to a Quakespasm coop game or host a game allowing Quakespasms to connect. This is part of rounding out the engine.
Source: moddb.com