Desmos : A free online graphing calculator that also includes a scientific calculator, and geometry tools.
Geogebra : A free online geometry software that allows you to construct, measure, and transform geometric shapes
CPM Tiles : A digital resource that features virtual manipulatives for base 10 blocks, algeblocks, number lines, and area/perimeter
Gapminder : A non-profit organization that has tons of factual-based data on random topics around the world
Random.org : You can perform random experiments such as generating random numbers, roll dice, deal cards, etc.