Shadow Warrior [official site] has never been my favourite of the Build Engine games (it’s Blood all the way for me) but that entire FPS era has a special place in my heart. It’s also worth nothing that Shadow Warrior is kicking Duke’s ass when it comes to remakes and sequels. As of today, you can explore the history of the original 1997 release by playing the alpha and beta versions of the game, which are now available free on Steam. The 1997 original has been free for some time, but now you can choose to play either the final release or either of the pre-release versions through the launcher.