ForcePAD is a very nice, little educational topology optimizing software. It is similar to Paint in terms of interface. You just paint a 2D structure with a brush kind of tool, place forces with few clicks and do the topology optimization very quickly. There is no elaborate modeling needed or meshing etc. Even an elementary school student can play with it and learn about topology optimization. Of course it is free too.
I did optimize something shape like Pikachu, and all from painting to end of optimization took less than two minutes.
