VSTO allows developers to create add-ins that extend the capabilities of Microsoft Office applications like Excel, Word, and Outlook. The current version is VSTO 4.5, which is compatible with Office 2007 through Office 2016. Using VSTO, developers have full access to Office object models and can automate tasks and customize the user interface of Office applications. iFourTechnolab offers VSTO add-in development services for Word, Excel, Outlook, and other Office products.