SUMMARY
Area 51 was a 2005 FPS which, in turn, was an adaptation of the 1995 arcade game of the same name. A few years later, the game was turned into ad-supported freeware. Apparently, there is an effort by someone named "Js41637" to make an open-source implementation of the engine. While the project is similar in nature to "OpenMW," the game data is apparently also included since the original game is already offered as freeware. At any rate, despite the 1.0 release version, it's unclear how much of the game is supported by the new engine: It appears that a lot of the multiplayer is supported but it's not as clear how much the single-player campaign is supported. At any rate, it's an interesting development for those who have the physical media but can't play it because of later incompatibilities between operating systems and copy-protection schemes. Enjoy.
LINK
https://github.com/projectdreamland - Project Dreamland, an open-source engine implementation of "Area 51" (2005)