Communication between apps and between Apps and OS
Currently apps are executed in sandboxes and there's no way to apps can work together. E.g. one app to look up information in the internet opens up another app that can scan barcodes..
The same is true for applications and the OS itself. Some kind of handlers on context menus of certain objects would be great. E.g. the context menu of images could list tasks provided by apps dealing with images. In more detailed/extremely simplified: What about having an app that rotates an image, an app that uploads images into the web and an app that is capable to send an image to the nearest printer.