Ion Radiant is the map editing tool for Daikatana.
Ion Radiant in action
It is used for level creation and level design. It requires an Open-GL 3D accelerator. It is made for TNT (Twin Texel) -based cards and accelerators, such as the Riva TNT, and will not work or have difficulty running on other cards. It has support for custom textures.
More information can be found here.