It's sort of like a budgeting app for credit card rewards. You link all of your spending accounts (they use bank-level security and don't store your login credentials), and Birch analyzes your cards and your spending. It will tell you how much you earned in rewards for each purchase, and let you know if you could've earned more using one of your other cards. You can sort your transactions by rewards earned or card used, and like any budgeting app, it also breaks down your spending by category.