絕地要塞
Some "Half-Life" modifications eventually landed on retail shelves. "Counter-Strike" was the most successful, having been released in six different editions: as a standalone product (2000), as part of the "Platinum Pack" (2000), as an Xbox version (2003), and as a single-player spin-off titled "" (2004), as well as in two versions using the Source engine. "Team Fortress Classic", "Day of Defeat", "Gunman Chronicles" (2000, a futuristic Western movie-style total conversion with emphasis on its single-player mode) and "Sven Co-op" were also released as standalone products. "Half-Life" is also the subject of the YouTube improv roleplaying series "Half-Life VR but the AI is Self-Aware" and "Freeman's Mind".