Is there a map maker tool for Doom like there is for Descent?

There is Tile System (google it.) Originally designed for Doom, and thankfully made easy to expand by third parties, it now has support both Doom and Descent, as well as a wide variety of other games. It's not an official map tool, but it's everything you could want from one.

The expandability of the TileSystem is incredible and very easy. It's what I'm using to create the various Advanced Campaign maps (added a ton of extra components). I've also completely converted it for a Castle Ravenloft map editor, and there's a really good Space Hulk tile collection out there too (harder to find). I highly recommend it.

-shnar

Until I can recover Doomedit from my broken laptop, I'd say tilesystem is a good alternative for now.