[oblio]

Funnily enough I was also looking for this unicorn recently.

I was aiming for Windows/Linux/Mac/iOS/Android.

In the end the two platform that were closest at the time (summer 2016) were HTML/Javascript and C#. Or C/C++ with OpenGL for the hardcore (not me!).

The real killer these days is the GUI toolkit. Ideally you'd want a SWT/Wx type wrapper around native widgets, most likely with a desktop flavor and a mobile one. Unfortunately nobody's investing in it, I think there's not enough money to be made. And there's no OSS community for it...

[pritambarhate]

Actually, there is an animal exists that runs on Windows/Linux/Mac/iOS/Android. Unfortunately, it's not as pretty as a Unicorn. It's an ugly hybrid with lots of raw power. C++ + QT (Qt Quick) + Something that looks like JS. I have seen one very complicated iOS and Android app made with QT with very good results. But the programmer was a very good with around 20 years of experience.