Left and Right Riemann Sums
This GeoGebra app lets you explore left and right Riemann sums and compare their accuracy to the definite integral. Try different functions and and move the endpoints to test how the accuracy of the Riemann sums changes.
Originally found at https://www.geogebra.org/m/SNS8SYSg but modified to do left and right Riemann sums instead of upper and lower.