Directly from wikipedia.
World Opponent Network or WON was an online gaming service, created by Sierra Games as the Sierra Internet Gaming System (SIGS). WON was used by games such as Homeworld, Half-Life, Star Trek: Armada, Soldier of Fortune, Dark Reign 2, Silencer, ARC and online versions of casino games.
Sierra was purchased by Havas in January 1999 and Cendant Software became Havas Interactive, which came to control WON. In March 2000, Havas Interactive merged WON.net with Prize Central Net to form Flipside.com. Regardless, games such as Valve Software's Half-Life continued to use the service.
In 2001, Valve acquired WON from Flipside.com and began to implement the Steam system in beta form. Over the next few years, as Steam was developed and tested, WON continued to serve.
Valve shut down the last of its WON servers on July 31, 2004, officially killing the remnants of WON. All online portions of Valve's games were transferred to their own Steam system. The announcement disappointed some of the long-time Half-Life and Counter-Strike players who held it in high esteem for being, in their view, more efficient in terms of speed and system resources than Steam.
After the shutdown of WON, some players continued to run a patched version of the retail versions of Half-Life or Counter-Strike, which connects to a WON replacement called No-WON (or WON2), and allows users to use the original server browser to connect to Half-Life servers, and their various mods (including Counter-Strike 1.5, and a Steamless version of 1.6), much as they could before WON's shutdown.
Since its shutdown, users who try to connect to WON in games such as the retail version of Half-Life will receive an error message.
