columnar is a Rust library for columnar representation of Rust data types. It provides a `Columnar` trait and a derive macro that transform ordinary structs and enums into columnar storage: each field is stored in its own typed vector, and enums store tags and payloads separately. The crate supports recursive/tree-structured enums, all-unit enums, `no_std` environments, and optional serde serialization. It is a library, not an application, with no web or CLI surface; the primary entry points are the derive macro and the `Columnar`/`ColumnarVec` traits.