• Sierra: Half-Life: Opposing Force   - Official site includes game overview, news, media, support, forum, demo download, and online ordering.
  
  
• CNET - Includes a free demo download and user opinions of the game.
• GameGuide.com - A complete game guide including first-person shooter basics, weapons descriptions, walk-throughs, cheat codes, and easter eggs.
• Justice for all [JFA] - Includes screenshots, pictures, profiles, and downloads.
• Planet Half-Life: Opposing Force - Walkthrough, tips, downloads as well as strategies for both the single player and online multiplayer version.

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