Koa is described as 'Expressive middleware for node.js using generators via co to make web applications and APIs more enjoyable to write. Koa's middleware flow in a stack-like manner allowing you to perform actions downstream, then filter and manipulate the response upstream' and is a Web Framework in the development category. There are more than 50 alternatives to Koa for a variety of platforms, including Linux, Mac, Windows, Self-Hosted and Web-based apps. The best Koa alternative is Django, which is both free and Open Source. Other great apps like Koa are Supabase, Angular, Firebase and Ruby on Rails.