Half-Life や Counter-Strike が無料でできるようになったらしい．

Steam でできるゲーム

  Half-Life
  Counter-Strike
  Team Fortress Classic
  Deathmatch Classic
  Opposing Force
  Ricochet
  Dedicated Server

Reference

  Welcome to Steam (Official site)
  http://www.steampowered.com/
  Download
  http://www.steampowered.com/?area=getsteamnow