Fallout 2 Maps Editor by Dims
I am currently working on a more modern and multiplatform map editor called GECK. Dims Mapper is a great source of knowledge about the Fallout 2 map handling but in my opinion it is very clunky and would be hard to maintain.
If you really want to work with Dims Mapper make sure to read this forum thread about some issues you may encounter: https://www.nma-fallout.com/threads/dims-mapper-troubleshooting.220757/