Riemann is an Android application developed by MateSimple. The app allows you to calculate the approximate area under the curve of any of the included functions. The calculation algorithm is based on the LEFT RIEMANN SUMS method. The more rectangles (n) you choose, the better the approximation to the exact value of the area under the curve in the given interval.

The interface is user-friendly and easy to navigate. It offers a variety of functions to choose from, and the app provides a step-by-step process for calculating the area under the curve. The app also allows you to save your calculations for future reference. Riemann is a free app and is a useful tool for students and professionals in the field of mathematics.