https://mathsbot.com/?fbclid=IwAR28gicJJGzldoXKMvozvP5hCUOJPaDKScWJo7yWC72wQA0O7YWHbtucr-A#Manipulatives
https://www.didax.com/math/virtual-manipulatives.html?fbclid=IwAR2VvaW4d9XNUNn4quAA02U1zNooccezzABp0p5o9bgBcLiGlOzOEOBOf2w