Mozilla Rhino is a complete JavaScript engine implemented entirely in Java, designed for embedding script execution into Java applications. It provides a full ECMAScript runtime, including ES6+ features (BigInt, Promises, typed arrays, classes, modules), E4X (XML) support, LiveConnect (Java-JS interop), and a JSR-223 ScriptEngine implementation. The architecture is modular, with separate modules for the core engine, tools (shell, debugger, compiler), XML support, and Kotlin integration. The engine supports multiple execution modes: an interpreted bytecode (interpreter v1 and v2), a just-in-time compiler via the optimizer (using jdk.dynalink), and a classfile-based compiler. Key entry points include the `Context` class for script execution, `RhinoScriptEngine` for Java scripting API, and the `Main` shell tool. The project is well-tested with thousands of regression tests, test262 conformance, and JMH benchmarks. It is actively maintained, with recent releases and CI pipelines for Gradle and Bazel, targeting Java 17+ and Android.