koa-router is a mature, Express-style router middleware for the Koa web framework. It provides a clean API for defining routes with HTTP verbs, named routes, URL parameter extraction, nested routers, and automatic OPTIONS/405/501 responses. The library is built around two core classes: `Router` (manages route registration, middleware composition, and dispatch) and `Layer` (handles path-to-regexp conversion, parameter matching, and URL generation). The code is well-structured, thoroughly tested, and has been widely used in the Node.js ecosystem. However, the project has been largely superseded by the official `@koa/router` fork maintained by the Koa team. The original repository shows signs of stagnation: CI targets very old Node.js versions (6,7,8), dependencies like `path-to-regexp` v1 and `koa-compose` v3 are outdated, and there are 82 open issues. While the core implementation remains functional and the code quality is good, the library has significant technical drift and is not actively evolving. It is best suited for legacy Koa projects or as a reference implementation for router design.