Have you noticed that you can right-click a web application project in Visual Studio and convert it to a provider hosted app? Well why not? Basically your own website and a SharePoint manifest is all what you need for a provider hosted app. This discovery today made me think about all legacy web apps out there that can be converted to SharePoint apps.  Traditionally we had to add plain links to external applications or embed them into an IFrame by hardcoding it in an .aspx page or a Page Viewer WebPart. A web application that should be converted to a SharePoint app can be any web app, not only asp.net web site. For a year ago, I had a little nodejs project to try out mongodb and knockout.js: Anvaska which I published as a heroku app: