SharePoint 2013 introduces a whole set of new and improved features. One of the things that is both new and vastly improved is the Workflow platform. Workflow is no longer a part of the SharePoint core infrastructure, but instead a separate server product. Even though ye olde Workflow platform, 2010 style, is still in the product for backwards compatibility. SharePoint 2013 leverages the Azure service called Workflow Manager 1.0. (Not the cloud version but a local on-premises installation).