A dress selection experience integrated to Salesforce.com data
Ever since we released the WADL Generator tool (in alpha) for Siena, it's become easy to get Project Siena to work with Salesforce.com.
See https://channel9.msdn.com/Blogs/Microsoft-Project-Siena/App-Tour-Salesforce-Dress-by-Color for an app that delivers a novel fashion selection experience, with the key product data coming from Salesforce.com.
Also see http://www.wadewegner.com/2014/08/build-a-windows-8-app-for-salesforce-with-no-code-using-project-siena/ for how Wade Waggoner built a Siena + Salesforce.com app, including insights about the required WADL.
This is an exciting development, as it opens the window to an even larger number of apps.