What to use for rapid development of cross-platform applications?

Question

User interface

What programming languages, technologies, approaches, whatever need to be used for the rapid development of cross-platform applications?
I can partially answer on my own - an example for answering a subject can be node-webkit. And everything would be fine, and even excellent - there are a lot of JS programmers, everyone knows HTML and CSS, programmers are cheap, development speed is high, but the problem is that it is difficult to hide the source application code. or simply impossible. *By the way, maybe it's better to dig in this direction?*
On the other hand, you can use the same C, where I will get full control over the application, widgets and interface elements - but in this case, the speed of development and test coverage falls unacceptably low, and the cost is clearly increases.
I can also use Python or Golang. In this case, I get development speed, cross-platform, simple search or retraining of programmers. However, as far as I understand, I do not have the opportunity to write my own widget or radically change an existing one.
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PS: Using nwshapshot to generate VM bytecode from JS sources reduces performance by 30%, doesn't always work, and if it does, it only works with small JS files. That is, an application in which 5 - 8 libraries plus the working code can no longer be compressed.
For reference, you need the ability to create frameless applications with a completely custom set of UI elements. That is, as the artist draws, the application should look like that. Without frames and titles of the OS window, with its own progressbars and poetesses

Answer 1

Use Go in conjunction with Qt or wxWidgets. If Qt, then you can play with QML. And with wxWidgets, in my opinion, it's easier to work if you don't need your own widgets.

Answer 2

D + vibed
Very good option.

Answer 3

Main approaches:
1. Java
2. Qt Framework

Answer 4

my 5 kopecks for knowing:
1) +1 for C++\Qt .
in version 4.5 was the coolest SDK with the "smoothest" well thought out class structure. IMHO, of course, but I would even say that against the background of Qt, in terms of the harmony of the API - Java SE looks like a crutch-patchwork quilt (although it is understandable - Java has the most severe backward compatibility requirement up to Java 1.0, and Qt4 classes were "again " were designed in 2004-2007 without maintaining backward compatibility)
+: extremely well thought out, non-patchwork SDK. 90% of interfaces use the same logic and approach. up to the same function signatures for classes.
+ : most of the mechanisms of GUI-classes are sharpened for office applications.
- : not all classes are completely cross-platform. For example, Bluetooth on Android has not yet been sharpened.
What they have done with QML now - alas, I don’t know the details anymore. Moved away from Qt when it was 4.8-5.0 (now Qt5.3 is relevant)
2) I am now making a Java application on LibGDX (for the reason described above with Bluetooth). LibGDX is, in general, a game engine - you work with the camera, place objects/rights/elements on the plane yourself, and so on and so forth. Therefore, if you need to make a lot of menus and other things - at the very beginning, until you make your own layer of menus, buttons, headers - you will need to invest a little more than with Qt, but then you can do a lot more, more beautiful, more dynamic with effects.

Answer 5

AS3+AIR/Flex.
One code without porting is exported to binaries for each OS and works on Win/Linux/Macos/Android/iOS/Blackberry