Koa is a new web framework designed by the same team that created Express.js. The goal of Koa is to be smaller, more expressive, and a more robust foundation for web applications. One of the key features of Koa is the use of generators, which is a feature found in other popular programming languages such as Python, C#, and Ruby, and it is coming soon to JavaScript with ECMAScript 6 (the next version of JavaScript). Generators prevent the standard callback hell that is so popular with the development process in Node.js. As Koa is so lightweight, it does not come with any middleware out of the box. This is by design so that the choice of how to implement certain features can be left to the developer.

The Koa website (http://koajs.com) is shown in the following screenshot:

More information about Koa can be found on its website as well as its official GitHub repo at https://github.com/koajs/koa.