The above images are actually mini-Bilibos. They are like little plastic shells that are easy for toddlers to hold onto. They also come in a larger size that a kid aged 2-7 years old could sit inside. They are marketed as an "open-ended toy that stimulates the imagination."
Today we used them at Rosie's music class. Banging two of them together makes a sound like a horse clop-clopping along. They also look good for putting things into (today it was the little egg shakers), hiding things under, peeking or poking fingers through the holes, floating in the bath and a myriad of other options. They also claim to be 100% recyclable.
Occupational therapists love these kinds of toys. Of course I am hooked. I will be buying some for work and will be suggesting to family members that they might wish to buy some for Rosie for Christmas as well.