So I just talked about the Arduboy, which is a simple open source handheld console. This is a little more than just a tech demo, and is in fact a fully fledged thing. That's cause it's just straight up Triple Triad, from Final Fantasy lol. This is Triple Triad from FF8 and FF14, put in single player card game form. Play games, winning cards and money from your opponent. The difficulty of your opponent is equal to the number of cards you have. Buy new cards with your money, and also spend it on changing the rulesets!
How does Triple Triad work? It's a 3x3 grid, and you each have 5 cards. You then take turns placing down cards, and if you place a card next to a card, and your number is bigger, you flip that card to your side. Whoever has more cards by the end wins, with some leeway to the person who went second cause they get to place less cards. Ruleset changes change things up a LOT. You can have rules like uh, you choose a random card to play each turn instead of being able to choose which one. Rules where one of your cards is swapped at random with another one, which can be wild if you're REALLY lucky and get the card that's like, all aces.
And that's about it! I found this game extremely frustrating for the first hour, because the balance is kind of off and your starting cards are dogshit, then you're in a bit of a better situation, and you can sloooowly grind up. Then I grinded up money to get the #1 best card, and I ended up winning every single game and never lost again. It's a thing that's kinda weird as a little single player game like this, but I wanted to play a card game, and triple triad was kinda fun in FF14, so...
Not sure it was really worth the ten hours of grinding though lol