Localhost
A lot of apps are built using hybrid app development frameworks that use one big WebView for providing app developers a native wrapper and some plugins for their Web app. The web content is often bundled and served within the native app. For a couple of reasons using the file: protocol to access web content is no longer an option and WebViews provide APIs to host content.
See more in usage and challenges.
WebView2
Windows
WebView2 has a variety of ways to work with local content - intercepting web resources as they’re requested, mapping a hostname to a folder on the user’s filesystem, or registering a custom URL scheme. You can find details on all of these in WebView2’s documentation for working with local content in WebView2 apps.
ArkWeb
Arkweb allows serving local resources through $rawfile() mechanism and ://rawfile/ protocol. The second method for providing local content is to intercept ArkWeb’s network resource requests via the onInterceptRequest event. This event is triggered whenever ArkWeb needs to load a resource. The application can construct a WebResourceResponse using local resources and return it to ArkWeb, as described in Customizing Page Request Responses.