A free app for Android, by Jack Yu于.

RPN Plus Financial Calculator is a simple and convenient application for financial calculations. It is intended for both personal and business use. With its simple and intuitive interface, users can easily and quickly calculate their desired results. This app is a one-stop solution for all your financial calculations and can be used as a financial calculator, mortgage calculator, loan repayment schedule, interest calculator, and more. 

In addition, it is a great tool for anyone who needs to perform more complicated calculations such as calculating the amount of a down payment, the monthly payment for a mortgage, or calculating the profit for a business.