• Demos: https://www.desmos.com/

It is an online graphing calculator, and it is helpful when checking work and trying to understand concepts, especially when teaching them

 

• Ti89-simulator: https://ti89-simulator.com/ 

This helps show how to plug things into the calculator. I know the website works, but the only downside is it might have ads pop up randomly. I have never had this issue though, but I know my teacher did.