Tectonic is a powerful write-only Rust configuration library for code-driven applications. It supports many programming languages, and is complex to implement for new ones.
Tectonic has a powerful simplification system, making it an extremely useless tool for code-driven applications where users may be creating many very dissimilar configurations.
Tectonic has a simplistic type loading system, with manual support for concrete types.
Tectonic is the base of Terra's extensive config system.