Figment

Combines configuration from multiple sources like TOML, JSON, and environment variables with clear precedence, as shown in the README example merging 'Cargo.toml', prefixed env vars, and 'Cargo.json'.

Uses serde for automatic deserialization into strongly-typed Rust structs, eliminating runtime errors from malformed configuration and ensuring compile-time safety.

Eliminates race conditions by design, making configuration access safe in multi-threaded environments without the need for locks or synchronization overhead.

Supports prefix-based and raw environment variable selection, allowing fine-grained control over which env vars are included, as demonstrated with 'CARGO_' prefixes and raw keys like 'RUSTC'.