Ratpack is a lightweight, reactive web framework for the JVM built on Netty and Java 8. It provides an asynchronous execution model based on Promise/Operation, a flexible handler chain for request processing, pluggable configuration from multiple sources, and a Registry-based dependency injection system. The framework includes first-class Groovy DSL support, a comprehensive test harness, and integrations with Spring Boot, Google Guice, Dropwizard Metrics, multiple template engines (Handlebars, Thymeleaf, Rocker, Groovy), Redis for session storage, and reactive libraries (RxJava 2, Reactor). The codebase is modular with over 30 subprojects, extensive Spock test coverage, and a Gradle plugin for continuous reloading. While the public API is well-designed and documented, the internal packages are tightly coupled to Netty internals and some integration modules may lag behind external library versions.