DEU's Texture Companion (deutex) is a resource editor that can extract and insert graphics, sounds, levels and other resources in doom-format WAD (where's all the data?) files.
Deutex is command-line oriented and is most useful for assembling WAD files as part of a build procedure, such as via Makefile.
Games/freedoom uses deutex upstream as part of the build process. There are some plans to rework the Freedoom source package to be closer to the upstream process.