You are correct(sort of), although just ever so slightly earlier it started out as the replacement multiplayer lobby system for the GoldSource Engine, replacing the WON network system(which either got shutdown or Valve stopped paying for it, I forgot). I vividly remember the final patches for the WON system, after which only the most recent versions appeared on Steam for games Like Team Fortress Classis, Day of Defeat etc.
Originally Posted by groovychainsaw
Actually, reading the history I must have started using it somewhere in 2003..
EDIT: Found this on a Steam badge:
Years of Service
Unlocked: 21 Feb 2013 @ 11:49am
Member since 21 February 2004.