It is an assignment rule. An app builder is an application that is more like a mobile development tool, which makes use of hyper-productive development encironment which allows the developers to create applications that can work effortlessly on various operating systems such as IOS, windows, and Android.
An app builder shares one HTML5 code base, which allows developers to work over all platforms. Furthermore, the debugging tools that are built in, allow the developers to make use of the operating system and the hardware to develop the application. For instance, a developer can create IOS app using Linux or Windows, and can make a windows app using a mac computer