I'm thinking about tree structures, and I feel that I don't like them. It's like when you have a shop, then you try to put all products to tree-like catalog, and then you need to place one product to multiple categories, now you have multiple routing, bla-bla. I don't feel like everything in the world could be put to a tree.

Instead, I like idea of tags. I would like to store everything with tags. With tags I could do much more. I can even simulate trees if I want. I want to have tag-based filesystem!

But hey - modern OOP paradigm with inheritance is based on tree. I want to see how it is when you don't have such basement.

Closest thing I found is mixins in some languages. Do you know what else is also about this ideas?