Illuminations is a project designed by the National Council of Teachers of Mathematics (NCTM).
You will find many excellent Interactives on this site.
Search the Illuminations site by age and by topic area.
Each Interactive includes clear instructions, check Geometric Solids, for example, scroll down for full instructions on how to use the interactive. Questions for exploration are also provided.
Further examples, this is a great collection, try for example…