A few months ago, as a writing exercise to help me get out of a creative slump, I attempted to write the "worst" game system I possibly could. I like minimalist games combat-lite games. This game's systems were as convoluted as possible, written in a verbose first-person perspective, and included a very strange tic-tac-toe inspired card-based combat system. I found the whole experience helped me break out of habits, and examine what I like/don't like about games. But I still don't have much interest in fleshing the system out beyond scribbles in my notebook.
But it still has a framework and terminology I can reference back to in an adventure. So basically, I plan on writing an adventure for the worst system I could think up.