The following information appeared in an article written by Tom Warren on The Verge:
Microsoft is planning to allow developers to create “Agaves” web extensions to bring third-party functionality to Office clients. Web developers will be able to create an area within an Office application that lets webpages interact with documents and augment content with extra features. The Agaves will be provided through Microsoft’s Office Marketplace, or from private stand-alone Agaves at organizations.
Microsoft’s next-generation of its Office productivity suite, will support the new web extensions throughout a number of its core client apps. Excel 15, Word 15, Outlook 15, and Project Professional 15 will all support Agaves, and Microsoft will also allow Agaves to run on the Excel, Outlook, and Mobile Outlook Web Apps. The software giant is creating three different ways that Agaves can be integrated into Office applications: Task Pane, Content, and Contextual.
A Task Pane Agave will enable Office users to see an extension side-by-side with an Office document, allowing users to look up information from a web service based on a product name highlighted in a document. Content Agaves will allow webpages to become part of a document as embedded content that can be shown in line with documents. Developers could use this functionality to integrate a YouTube video clip or a picture gallery. Contextual Agaves will work on the Outlook side of Office and allow developers to display content with a particular mail or calendar item.