Is there a formal format for documenting the game design process?
Before you answer with "The Game Design Document (GDD), of course!", in my opinion (and lots of people's opinions as well, I think) a GDD is used for presenting a finalized product, and not documenting the actual game design process.
What I need is a tool to aid me in the process of designing a game. It has to have some sort of categorization of ideas (e.g. in the set of elements that Greg Costikyan has proposed, it could have sections for goals, resources, challenges, etc., although it doesn't necessarily have to fit Costikyan's ideas), it has to be aimed towards the iterative design process (which means that it has to have inherent non-linear capabilities, non-existent in the GDD format) and it has to be as universal as possible (suitable for both video games or board games).
If such a tool doesn't exist, I propose to start a collaborative effort from the game designer community, working towards creating it, producing a tool that's as standard and universal as possible.
P.S. Although the formalization of the game design process has been proposed several times, the closest I could find to a formal format is this document.