Here are a few materials my brother and I made for Finn.
Washers on a horizontal and bendy metal dowel. It's hard to hold the washers upside down and push up to get them onto the rod!
Interestingly, the cubes of this material were unpainted for many months, and Finn didn't pay any attention to it. It was only when they were painted that he started using it. It's the first material with which he has shown real concentration and repetition. We also sometimes tape the whole thing onto the side of his shelves so the dowel lies horizontally for more challenge.
My brother made this amazing puzzle for Finn. It's really fantastic as all the pieces are interchangeable. Finn loved taking all the pieces out to reveal the family photos underneath ever since he was tiny. Now I can ask him where grandad is and he will try hard to remember before lifting a piece out. I thought about changing the pictures from time to time but he really loves these ones.
Cubes on different sized dowels. Oh that's hard! He is still a bit young for this one at 18 months. There are two cubes for each dowel so he can't just stack them all on the small dowel.
Different sized circles. He can be deeply focused on this one.
Fantastic one shape puzzles my brother made! We put pictures of him underneath to play peek-a-boo.