Give me the monies
Sending and receiving money between friends is incredibly easy. It is like the PayPal network, but with a superior UI and no fees. Admittedly, it cheats a bit here as PayPal is fee-free if your money is within their network already and that is the only way to work with Monzo.
Track my cash
The application does a great job of giving you the basic information you need up front (balance, spend for the day) and sorting your spending into groups so you can see with horror quite how much you're spending on eating out. You can access this information by month, but more importantly you this is all available via a simple API.
The API is where the fun starts. I'm not going to apologise for liking data and graphs and it's really nice to be able to start plotting my finances in different ways to get to grips with the patterns to my spending (and remember how to do data manipulation and visualisation).
|Scales redacted :-)|
If you want to have a look you can get the code from Github.