With Office and SharePoint 2013, you can now build a new class of apps that extend and personalize the way we create and consume information.

Develop apps as web applications. You can use HTML and JavaScript for client-side code, and your choice of language for server-side code, such as VB.NET, C#, or PHP. Use your favorite tools and hosting environment to develop, test, and deploy your app.

Apps can interact with Office thanks to a new JavaScript API, consistent across multiple Office applications. Take advantage of OAuth support in SharePoint, along with a new set of REST APIs, to connect and interact with SharePoint while hosting your app in the cloud. See this 30 minutes video to gain insight of Office Developer Tools for Visual Studio 2012.