I'd like to have the Nokia Refocus App for Android.
I haven't found this feature anywhere yet: Just tap anywhere on the finished image to refocus it. The option for color pop was also great: tapping on a color in a specific area of the photo remains while the rest of the photo becomes black and white.
Refocus was unique in the sense that it didn't use any unique hardware to achieve the functionality, instead it is a pure software app that created similar results as Lytro (which will be acquired by Google). It is probably not as good as a real Lytro camera, but it was second best.
I am not sure whether HMD need the old Nokia IP. I guess they'd need to completely redevelop the app.
I don't think the app would need to be rewritten but would need to be refactored to run on Android instead of Windows Phone, which may or may not require a lot of work (probably a lot). But would be worh it.
Whether or not they need the actual IP depends on if there are any patents associated with it. HMD have been getting some of the patents from Microsoft so maybe they already have them.