Developer: Monolith Productions
Release Date: May 21, 1997
Source Code Release Date: Not formally released
Blood is another first person shooter using the same Build engine as Duke Nukem 3D, but with dark gothic horror elements and weapons featuring alternative fire modes. It enjoys a cult following and the source code was never officially released, but modern Build engine ports do a decent job with a reverse engineered version of its gameplay.
Note that you will need the original Blood files, not the ones from Blood: Fresh Supply, which is an updated edition. Digital retailers such as Steam and GOG feature the updated edition for sale but they both come with the original as well, which is the one whose files you want. GOG lists this in your library under the title Blood: One Unit Whole Blood.