A solo RPG based in tarot readings. Beautifully designed, simple to play with no learning curve and tons of room for interpretation and creativity. I have this printed and pasted in a journal specifically for the game.
I've played four campaigns with this system now, as both player and GM, and I've had a blast every single time.
Admittedly took me a little longer to play than what the guide suggested, but I was also writing prose for each turn. I had a ton of blockages in my game and still found the game super enjoyable.
I was a player in a Sentai campaign a while back. I never even saw the full book and only used the character sheet, and still found the system intuitive and fun to play with.
Ran a campaign in this system, which then inspired three other campaigns. A bit of a learning curve in terms of character creation, but pretty fun.