Mathigon
From WikiMathCom
Mathigon is a web-based interactive book with activities and courses about mathematics for children and self-learners.
Polypad
Polypad is a tool included in Mathigon consisting on a board playground that the user can use to create shapes.
Features Polygons, 3D solids, folding/unfolding polyhedra, geometric visualizations of numbers, fractions ...