Nova is a custom ECMAScript (JavaScript) engine implemented in Rust, designed as a modular, embeddable runtime. It features a full bytecode compiler and virtual machine, a custom mark-compact garbage collector with typed arena allocation, and a shape-based (hidden class) object model for property access optimization. The engine closely follows the ECMAScript specification, implementing built-in objects (Promise, Array, Map, Set, Proxy, Temporal, etc.), module loading, and concurrent agents. Its architecture emphasizes data-oriented design and safe GC interaction through Rust-specific patterns like `GcScope`/`NoGcScope` and the `Bindable` trait. The project includes a standalone CLI (`nova_cli`) for running scripts and a test262 harness, currently passing approximately 80% of the official test suite. While actively developed, the engine has known limitations: many features are incomplete or behind feature flags (e.g., RegExp lacks full compliance, Temporal has placeholders, and several built-ins have `todo!()` stubs). The codebase exhibits high craftsmanship in its GC safety system, bytecode compiler, and object shape mechanics, but relies heavily on unsafe Rust and manual lifetime management. Nova is primarily a research-grade implementation aimed at embedding and exploration, not yet production-ready for general use.