Web applications are typically composed of two parts - the client part, that works in the user browser, and the server part, that runs on some kind of a network server. The client part is responsible for creating GUI (graphical user interface) and interacting with the user. The server part takes care of the business logic (data manipulation, data storage, math calculations, business processes and so on). There is a huge number of different solutions, that allow developers to build such type of applications, but even the most popular suffer from some serious problems and limitations.
The client side of the web application is most often built with JavaScript, HTML and CSS. This alone means three different programming languages. And the server side is usually built using yet another language e.g. Java, C#, PHP or Python. This is a well known problem and the popular solution is to use Node.js on the server side and create fullstack applications with JavaScript only. It's nice, but it has it's own limitations (single-threaded architecture, scalability, medium quality of many npm packages) and is not satisfactory for everyone.
Other solutions are based on modern JVM languages compiled to JavaScript (Scala.js, Kotlin/JS). These are the relatively best solutions - you get the quality of the enterprise class on the server side and the same language on the client side.
This is how KVision works - it allows you to build whole applications with Kotlin language only. Everything is compiled and type-safe. No knowledge of JavaScript, HTML or CSS is required.
Both parts of the web application are typically completely separate from each other. On the server side an endpoint is just a routing definition (an URL) with some parameters and body parser. On the client side it's just a XmlHttpRequest (or jQuery) call. But, because of typeless natures of JavaScript and HTTP protocol, there is no strict interface, no contract, between the two parts. A change made on one side does not force the developer to make a compatible change on the other side. Someone always has to remember about it during development and maintenance of the application. And the inevitable errors are expensive, because they appear only at runtime (and often only in the production environments).
KVision is the only framework that allows you to define a type-safe and compile-time checked contract between the client and the server part of your application.
The asynchronous architecture of JavaScript environment and XmlHttpRequest forces developers to use callbacks when the client part need to communicate with the server. These callbacks make the code look complicated, hard to understand and maintain. With many callbacks you can even end up with so called "callback hell". You can keep some guidelines or you can try to use promises / async functions, but a big change is only introduced by the Kotlin coroutines.
The architecture of KVision server-side interfaces is heavily based on coroutines, wrapping asynchronous client-server callbacks into easy-to-read synchronous-like code.