Microsoft announced today that the Office Developer Tools for Visual Studio 2012 are now available, allowing developers to create apps that target Office 2013, SharePoint 2013 and Office 365. Developers can also optionally create apps for Office via the web using a technology previously codenamed “Napa.”

Apps for Office and SharePoint extend Office 2013 and SharePoint 2013/SharePoint Online (part of Office 365) in useful ways. Both types of apps are built with popular web technologies such as HTML5, CSS, JavaScript, REST, OData, and OAuth, Microsoft says.

Apps for Office come in three categories: Task pane apps that appear in the task pane of an Office application, content apps that appear inside of the document’s content, and mail apps for Outlook 2013 and Outlook Web Access, which appear next to an open Outlook item, such as an email message, meeting request, meeting response, meeting cancellation, or appointment.

Apps for SharePoint extend the capabilities of a SharePoint web site. Users can discover and download apps from the SharePoint Store or from their employer’s private App Catalog and install them on their SharePoint sites.

Developers have two choices for creating these apps:

Microsoft Office Developer Tools for Visual Studio 2012. This free add-on for Visual Studio 2012 installs a set of extensions—including new templates, new designers, and new integrated lifecycle tools—which let developers create new apps that run in Office 2013 applications or in SharePoint (2013 or Online). You can download these tools from the Microsoft web site.

Office 365 Developer Site. Developers can also create apps for Office in a web-based environment hosted in Office 365. Previously code-named “Napa,” this subscription-based online experience is being updating on a weekly basis, according to Microsoft. It consists of a SharePoint site in Office 365 configured for apps and the "Napa" Office 365 Development Tools. You can sign up for the Office 365 Developer Site on the Microsoft web site. The subscription costs $99 per year. But Visual Studio Ultimate and Visual Studio Premium with MSDN subscribers receive a one-year Office 365 Developer Subscription as a benefit, and Office 365 Plan E1 or E3 customers can provision a Developer Site as part of their subscription. A 30-day trial is available.

Developers interested in creating apps for Office should also follow Microsoft’s Apps for Office and SharePoint Blog and check out the Apps for Office and SharePoint Dev Center on MSDN.

Here's a video overview.