It's an app that helps you split bills with other people. Quite helpful if you have a lift club or shared accommodation.
For example, if Person A, B and C all buy $10, $20 and $30 groceries for the house, it will calculate who owes how much and to whom. Throw in extra bits like Person A borrowing $5 from Person B and it starts getting complex.
Oh, it's in the title of the post, not the post itself. Took me a while to scroll all the way up.