Themes and extensions are not new to Chrome; the store simply brings them together with apps to provide improved discoverability.
Outwardly, the applications might not seem all that different, but for those using the Chrome browser, Google has added a layer of functionality that app developers can take advantage of.
A different sort of web app.
Unlike standard web applications, apps in the web store are installed rather than simply linked to. This is more than just a semantic difference. Apps installed from the web store appear on the browser’s ‘New Tab’ page, have special security permissions and can be monetized.
Once installed, an app appears at the top of each new tab opened in Chrome.
Functionality here is pretty minimal (you can’t yet reorder your applications), but it makes these applications more visible and easier to return to than others.
App creators can seek special permission for their applications. These permissions appear (a bit too discreetly) on the applications details page.
Chrome allows applications registering for particular features to make API calls without prompting the users for permission. For example, when a web application normally tries to access the user’s location, the browser will first prompt the user and ask for permission. For an application that has registered for the right to access your location, Chrome will allow it make those calls without any additional permission. Applications can register for access to geolocation, notifications and unlimited storage space.
People pay for Apps, right?
Certainly the most compelling feature of the store’s installation model is the integration with Google Checkout allowing developers to charge for their applications through a centralized payment channel.
Apps in the web store can be sold for a one-time price or through a subscription. Developers can also opt to charge for extended functionality or content within their applications with in-app purchases. Google even provides a try before buying option for developers to easily allow free use of their application for a limited period of time.
To limit application to paying customers, Google provides an API that verifies that a visitor is authorized to access your content.
Two types of apps.
Apps is that they come in two flavors: hosted and packaged.
Hosted applications are web apps hosted on a web server. They include metadata that provides the information necessary for the store to list the App and for Chrome to manage it.
Hosted applications have access to all the features I mention above, but packaged applications are more interesting for a few more reasons.
Files for packaged applications are bundled into a compressed file that is downloaded by Chrome when the application is installed. This greatly simplifies the process of providing an application that will work when the user is not online. Furthermore, developers can upload the package to the web store to host, eliminating the need to manage their own servers (unless they are directly providing dynamic data for the app).
Packaged Apps also have access to Chrome’s extension APIs. These APIs allows developers to add UI elements to Chrome’s UI. Packaged Apps are actually hybrids between web applications (pages with in the browsers window) and conventional extensions (UI within the browser’s chrome)
For more information about the store, see Google’s Documentation.