I had an idea for a saving system for TU, not as in saving your game, but saving units.
Set goals, give them names and the amount of units you want to save, and then a percentage of units it takes from gameworlds, selling objects, achievements, and fishing, what transactions it takes units from, and whether or not you want to be able to take out money mid-goal.
So you can set a goal for maybe a new Condo that you want, set the name of the goal to what you want, change the percentage of units it takes from transactions, such as 25% of units earned, and what transactions it takes from, maybe you only want it to take units from gameworld wins, and nothing else, and you could set it to not allow you to take units out of it until its 100% filled.
Maybe instead of just a GUI accessible from the menu it could be a use for the Piggy Bank item. Making it either a new version that’s free to get, or a very low price one you can buy from the Toy Stop (5-10 Units?). Sparkling as it gets closer to the set goal, and at the end you can press interact on it and it will smash open and give you your saved up units.
I however don’t know how hard this would be to implement, or how janky it might end up being, so take this with a grain of salt.