Thank you so much for the kind words, and for taking the time to post! I really appreciate it.
So the entry I made is an adventure for the MÖRK BORG tabletop roleplaying system. It's a roleplaying game (RPG) just like D&D is an RPG, but uses a very light ruleset, and has a rather dark and "heavy metal" setting. Picking up the rules either in print or PDF would be required to play. Although I bet you could use the rules summary and some online generators, and maybe play without buying anything!
You post really made me think about how that may not be obvious to everyone, particularly in this game jam (which is mostly digital games). I plan to update the game page description to make this more clear. I also plan to include some information about that on all future ones as well, as a best practice.
Again thanks for pointing this out! I'll make some changes.