Before answering your question I wish to share the differences between Sharepoint Foundation and SharePoint server.
SharePoint Foundation requires no licensing and is essentially free. There will be hardware, deployment, and other miscellaneous costs, but no licensing costs. That is a huge difference between it and Server.
Foundation provides basic site creation, document collaboration functionality just fine. And just that, is usually what organizations are looking for.
SharePoint Server adds various social, search, business intelligence, content management features to Foundation.
The apps for SharePoint provide a new method to deliver specific information or functionality to a SharePoint site. An app for SharePoint is a small, easy-to-use, stand-alone productivity app that solves a specific end-user need. Before you allow site owners to install apps in a SharePoint environment, you must plan how you want to support them. You have to determine your organization's policy around apps for SharePoint, plan your configuration settings, and determine how to manage and monitor the apps. This article discusses key decisions and helps you understand the choices to make as you plan to support apps for SharePoint.
For more Reference https://technet.microsoft.com/en-us/library/fp161237(v=office.15).aspx