ZDaemon is a popular online Doom port, which enables users to play classic Doom and extensions thereof over the internet, with people from around the world.

ZDaemon originally began as a continuation of the csDoom project in 2000, led by Sean 'ShadowFang' White, to deal with the csDoom's abandonment by its author. In early 2003, Nightfang left the team and his successor, Raider, continued leading the project from release 1.0 and onward. Since the beginning of ZDaemon's development, it has passed through 50 different releases, from 0.8 to 1.08.05, with a wide variety of improvements throughout. ZDaemon has the most refined networking code of any Doom port written to date.