At Build developer conference, Microsoft announced platform improvements on Windows Phone 8.1. App developers can now take advantage of improved multitasking, HTML improvements, Geo-fencing APIs, improved Live Tile, improved notifications and more.
Also, Developers now have access to Cortana for their voice based interaction UX. They can use Cortana for complex grammar based queries and more. Microsoft will be detailing these features in the developer sessions at the events at BUILD.