#30006, Internet On Fire Etc...
Some cursory searching has revealed that SDRadiant is the Splash Damage version of Radiant -
this pastebin claims it was for Wolf:ET! Certainly a curious choice of editor to still be using after all these years, but I suppose if something ain't broke, you shouldn't try to fix it.
Now, where you
get SDRadiant from is another matter... Does anyone know if it's packaged in the Wolf:ET download? It'd take me about four hours to check with my speed...