WAD Painter is a simple paint program that can be used to combine textures from WAD & PK3 resources.
Actually, it's a strip-off of the DD_TERRAIN tool, that keeps only the "texture painting" mechanics.
It was created in order to have a separate development path for possible future functionalities that could not fit the parent project.
Downloads: (version 1.1.3.27 - 20220103)
Executable (win32): https://sourceforge.net/projects/wad-painter/files/WADPAINT_1.1/WADPAIN