My most recent thrift store shopping has led me to a wonderful product called Zoob. These are interlocking plastic pieces like I have never seen before. Their unique shape and design give them countless possibilities. I was concerned that they would be too advanced for Star, but she seems to really enjoy them.
She is only able to connect them end on to end, but she is trying to learn how to cross connect them. I think it will be a little while before she can create actual designs from them. Right now, besides just playing with them, I am using them to reinforce concepts like shapes and her alphabet. I will construct a letter and if she correctly identifies it, she gets to break it apart. Right now she is totally into breaking things apart.
In my opinion, this is a wonderful tool for open ended play that will last for years and years. Here is the link to their official site. Zoob by infinitoy