I think you are kind of missing what the hard part is for many people, which is not choosing where to put the savings, it is choosing to save at all. Many live paycheck to paycheck, even go deep into debt on credit cards and payday loans. There's a whole broad class of apps like Mint, where it will show you all your costs and income and give you tips about how to reduce your spending, save more, refinance debt, etc..
Then there's a whole broad class of lifestyle apps that could be written, like a saving social network where you are socially rewarded for not spending a lot, win status in a game, etc.. E.g. maybe an app where you make a bet with a friend, if you spend under $100 on food this week, they owe you $100, and vice-a-versa. That would keep you both watching your spending and actually having something to save.