This appears to be a free service, but the code behind the API is not available.
Although, the one benefit for InvoicingAPI is that it gives an option to quickly give a payment code instead of having to send them to another payment application.
The Financial Modeling World Cup presents an elimination competition for expert Excel users. Every 5 minutes the player with the fewest points gets eliminated. This time 8 participants will show their Excel magic - Diarmuid Early, Andrew Ngai, Brittany Deaton, Michael Holmes, David Brown, Alana Reid, Isaac Lee, and Emilie Williams. Commentary starts at 5:03.