For modelling guns/characters:
Kinetix 3DStudio Max release 4 (version 3 also works)
RSE export plugins for 3DSMAX
For texture/graphics work:
Adobe Photoshop version 5 or 6, I have 7 but haven't tried it yet.
RSE plugins fo photoshop
For Hex editing, and changing texture assignments without re-modelling:
Kahei HEX editor, no longer available, but any HEX editor will work.
For text editing:
Windows notepad. I have never used IGOR to create any of the stuff I've done, I guess it's an old habit from Rogue Spear.