I found the French site via lilla a, where the children are using post-its on windows, creating patterns and designs. The material is open-ended if we think outside of the box and let children make the choices about how to use them. That natural light of the window adds to the appeal, I think.
There is so much we can buy for children to use, and so many ways that they can be instructed to play. the simplest things go the distance, though.