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.
The preserving and sharing of history in this way seems like a Good Thing all round, . You can read a detailed analysis of the beta version, which leaked back in the day, over on Hendricks266's site, which is as pleasingly oldschool as Shadow Warrior itself.
"Prototypes of games have always fascinated me. Shadow Warrior is no exception. The 0.90 "beta" was leaked by a tech support employee who wanted to play a modem game with his friend. Unfortunately, the game spread farther than his friend, and this employee was fired. One difference in this version is you begin the first level in a completely different location. There are also quite a few unreleased maps included in this version, which can be selected through the user levels. There is also a ton of unused art, and even some other good stuff."
There's something particularly fascinating about prototypes of Build Engine games. The finished articles often seemed like they were straining to contain all of the ideas thrown into them, and I'm interested to see how all of the elements were remixed or boiled down. For more of the beautiful weirdness of Build, check out our retrospective on the most nineties of engines.