This is the old EDuke 2.0 patch, repackaged as a ZIP file that can be unpacked on top of a clean installation of Duke Nukem 3D: Atomic Edition v1.5 for DOS.
It is based on files from two old releases, eduke20.exe (the original) and eduke20a.exe (an alternative one). It also (for most) removed the CD check.
You can have a look at README.TXT. For more technical details, see ECHANGES.TXT.
The file EDUKE.TXT is the original 2000-era EDuke readme. Note that at least a few of its contents might be out-of-date.