Visual Studio add-ins are deprecated in Visual Studio 2013. You should upgrade your add-ins to VSPackage extensions. For more information about upgrading, see FAQ: Converting Add-ins to VSPackage Extensions.
The Visual Studio Add-in project template enables you to create add-ins, which are extensions that add functionality to the Visual Studio integrated development environment (IDE). You can find this template in the New Project dialog box, in the Other Project Types / Extensibility section.