I try not to speak in first-person when I'm doing general site content, but Deathmatch Maker is a rather strange and unusual tool, one that I had to order specifically for this site since I couldn't find a copy online. In the interests of public safety during general operation, I present some notes from my experiments in it:
Textures won't appear unless you run the software in 256 colors. This unfortunately also makes it look rather ugly. (This should be apparent in the screenshots.)
Traditional WAD loading isn't a thing; the virtus.wad the program uses is hard-coded, but can be edited or switched out for any WAD you'd like.
The program expects to be in C:\VIRTUS\. You may want to extract the files below there. Otherwise the program might say it can't load any textures because "memory is low".
This program is rather useless without a manual, and unfortunately, the copy I ordered from Amazon didn't come with one. It's not often a level editor manages to confuse me, but I wasn't even able to connect a hallway to a room with it. It's also just generally slow to load and edit levels, even on a modern machine with 64-bit Windows.
If you have your taskbar on the side of the screen rather than the bottom, the program gets confused and spawns the splash screens and dialog boxes halfway off the top of the screen.
The grid is in increments of 10. You can't change it. This is something I didn't even notice in my testing and learned from a func_msgboard thread.
There's no "texture browser", just a separate HTML gallery of textures you're supposed to refer to. I guess you could rip the GIFs and use them to tile your Neocities site's background, if you're so inclined.
I've had visual glitches where two template sections right next to one another appear to be completely different sizes and distances apart. it's unlike literally any other 3D preview I've seen in an editor. The 3D renderer seems to glitch out constantly on modern computers, too, displaying geometry behind walls and generally looking awful. This doesn't affect the compiled levels.
This one's pretty much a historical curiosity and is absolutely awful and useless nowadays. Don't expect it to work like a normal level editor if you do try it. The entire contents of the CD are available for download below, or (because my copy wouldn't rip) you can get the CD image at the Internet Archive. As an aside, the company behind it, Virtus Corporation, apparently went on to form Red Storm Entertainment and make the Rainbow Six series. Go figure.
Virtus Deathmatch Maker (archived website) touts itself as the first id-authorized level editor for Quake and was sold as a proper big-box PC title in 1996. The program takes a unique approach to creating levels where template sections of a level can be dropped into the overhead grid and strung together, creating levels without the need to worry about piecing every bit of architecture together yourself. In fact, a drag-and-drop approach is taken with everything from placing enemies to texturing walls.
On the compiling side, Deathmatch Maker takes an all-in-one approach with a hard-coded set of compilers. The program also features importing and exporting in the traditional map format, however, so other compilers may be used if desired. The program comes with some new enemies and textures, featured in a custom progs.dat and WAD that also includes the textures of the base game.
Deathmatch Maker comes with two brand new example episodes that are fully playable as a partial conversion without the need for the program itself. These are also available for download in the "Supplementary Tools and Example Levels" download below. The sources for all of Virtus' example maps are packaged with the program itself, which the documentation notes are intentionally broken as a sort of "tutorial" on troubleshooting and level design.