Hmm, interesting. Having some trouble getting it running. I downloaded the latest package here: http://xlengine.com/downloads/
I downloaded the "XL Engine Release R2" and extracted it.
Then when I ran it, it told me I was missing OpenAL32.dll. So then I went and downloaded the OpenAL setup from here: http://www.mediafire.com/download/nwt3ilty2mo/oalinst.exe
Then I was able to run XLengine_Launcher.exe from the package and it worked properly (was able to see the interface). Clicked on Dark Forces, and then pointed the Game Data Folder to my Dark Forces install directory. Unfortunately though when I click Play the application crashes. I'm running Windows 8.1. Maybe you can try that and see if it works for you.
The error it gives me is an access violation, which could be 10,000 different things, unfortunately. The site does say it's an alpha release, so it's still very much in development. Let me know if you get it running though.