It's much simpler to write code for the Office apps store because we get to use the skills we already have being web native developers. And that means we can reach every version of Office from here on out with the same code that we already write for all major web browers.
-Poll Everywhere, Office 365 Partner
Apps for Office
An app for Office is a webpage you build and host inside an Office client application to extend what your document, spreadsheet, or email message can do.
Run them in:
Apps for SharePoint
Apps for SharePoint are easy-to-use, lightweight web applications that extend what your SharePoint website can do.
Use them as: