It's a library that allows you to visualize tree data structures in Rust with output like tree(1). For example,

Parent
├── Child 1
├── Child 2
│ ├── Grandchild 1
│ └── Grandchild 2
└── Child 3

This crate was extracted from ruut, a CLI intended for doing the same thing. See that repo if you're interested in executing a tree visualizer from the commandline or for something that can process common serialized data types (e.g. JSON).