Open web applications are those web applications that make use of open standard technologies, such as HTML5, CSS, JavaScript, and so on. These applications differ from native applications based on the fact that open web applications run on a web browser and hence can be accessed from a wide range of devices. These applications can be installed, access device hardware via the WebAPIs, and be run offline by making use of technologies such as AppCache and IndexedDB. However, these applications should be designed in such a way that they are cross-platform; if a device does not have all the hardware capabilities, then there will be a graceful degradation of the features of the application. Open web applications do not make use of proprietary technologies.
Let's take the example of Stack Edit (a web application), which is an online text editor that parses the markdown text and is very popular among authors. It is an example of an open web application. When loaded for the first time, it stores all its static data in the form of AppCache. All subsequent files that you store with the help of the in-browser text editor will be stored in the browser itself with IndexedDB. The application does not require a working Internet connection on subsequent runs.