For GunZ you'd use 3ds max 2010 or GTK radiant. GTK radiant is what people used when they didn't have access to 3ds max 2010 - 3ds max 2010 is superior, but also harder to use.
The reason I'm saying 3ds max 2010 instead of a newer version is because the gunz plugins only work on 3ds max 2010. You can also find gunz plugins for 3ds max 2014, but I cannot confirm if they work.