Oh boy do I have news for you! Xamarin [1] does exactly this. You write your app logic in C#, which is then AOT compiled to native code. You the write the UI for each platform using native APIs (although you can use Xamarin.Forms if you truly want the same UI across platforms). Xamarin supports Windows, macOS, Linux, Android, and iOS.

[1] https://visualstudio.microsoft.com/xamarin/

Sooo... wxWidgets and Qt? :)

https://www.wxwidgets.org/

https://www.qt.io/

If they really do translate to a fully native experience/look-and-feel on each OS, what's keeping them from being more commonly used?

Not a rhetoric question, because the answer is what needs to be fixed.

They do not translate to a fully native experience. At least on macOS, they stick out like a sore thumb.

And honestly, I think in the end, virtually any such tool will, because to really get the fine nuances and details right, the programmer simply must be aware of them, no automation will do this for you. On macOS, even Apple's own attempt on this ("Marzipan", which allows to generate iOS and macOS apps from a single codebase) suffers from this, although admittedly one may hope that at least in principle this framework could eventually really provide a 100% native experience, provided the people using it are aware if the idiosyncrasies of macOS (and conversely, iOS).

And that's for a tool trying to provide a common API for two UIs, with all three products developed by the same company. It gets much tougher once you also try to get Linux and Windows supported...

I've tried many frameworks that promised to this in the past 20 years, both as developer and user. All overpromised and underdelivered. Qt and wxWindows included. I actually prefer Atom (electron based) over any wxWindows or Qt software I ever tried - though this probably is primarily because somebody tried hard to polish its UI. While (I am guessing) most people who are content with what Qt and Wx deliver won't even notice the need to polish (those who do care eventually realize it is hopeless, and move on).

> what's keeping them from being more commonly used?

One of the reasons is the fact that they're written in C++ and not C, therefor difficult to wrap natively by host languages.

At least, that's my main gripe as someone who doesn't want to touch C++.

So if they were C, then one would be able to bridge almost "toll-free" with Swift/Objective-C on the Mac, for example.

There's libui, which is pretty good for traditional desktop widget apps.

But that's not what app developers are looking for. They want to be able to throw something together and have it just work and look as intended on any platform.

Ease of getting started is in my opinion among the 3 most important factors for developer adoption of a technology.

How stable is it? The readme says it's at Alpha 4.1 https://github.com/andlabs/libui