A simple option that is either separate or tied to the difficulty setting of the game would be somewhat easy to be able to turn on/off friendly fire.
So either a checkbox, or something like what was in Neverwinter Nights 'D&D Hardcore rules' which allowed FF, while 'normal' didn't.
I personally would prefer this to be an option presented at the beginning of the campaign, rather than a toggle option for whenever you want, so that when we make our own modules, we'll be able to provide that option as well, and/or force it to be enabled.
