Desmos
Desmos is a website for math teachers and students. For teachers, there are free lesson plans for all levels of mathematics. Students can also access these lesson plans for extra practice and use them as review. Desmos also functions as a graphing calculator, able to graph multiple functions at a time and execute complex calculations. This is an all-around great tool for teachers and students alike.
Geogrbra
Geogebra is a website that is a great tool for teachers and students alike. There are lesson plans accessible to students and teachers. This website also allows students to graph different geometric shapes and perform constructions, transformations, and much more. This is an overall great tool!