[nercury]

First and foremost, algebraic data types, specifically, proper sum types, called "enums" in rust. Think safe C unions or sane C++ variant. Everything is built on them, they help to encode various states and ensure they aren't misused.

Second, moves by default. They make building wrappers that depend on creation and destruction of a value much easier. They can track various things: memory usage, threads, temporary pointers, or whatever else. Unlike unique_ptr, they are on stack and part of the type system.