You can now build Windows 10 apps online thanks to updated Windows App Studio Beta
Things just got even more amazing with App Studio. Thanks to a new update, Microsoft is now allowing people to create a Windows 10 app via the Windows App Studio Beta creation tool. These apps are built using the new Windows Universal Platform, allowing you to generate apps for both Windows 10 Insider Preview and Windows 8.1 (including Windows Phone 8.1).
The updated App Studio now takes advantage of Live Tiles, Xbox Music Data Source, Bing Maps, Application Insights (an analytics service to monitor app usage and performance), and more. http://goo.gl/lJJcU3