I haven’t gone through all of them yet, but some of the notable ones I’ve seen so far are:

• Spoor (Lightweight free-form fantasy RPG system)
• Tiniest D&D (3 business cards, 2 with lightweight RPG system rules and 1 with quest generator)
• Wallet Dungeons (Build dungeons with d6’s)
• Lost Cities (Stand-alone adventure suitable for solo play)
• Pocket Planet Fantasy (Generate planetary systems for sci-fi adventures)
• A Long Walk Home (Minimalist meditative solo journaling journey using thrown dice to represent a map you travel)
• Blind Luck (Creative alternative to dice)

Let me know if you find other cool ones worth checking out! (it shouldn’t be hard)