dont know whether this is really related (maybe just the name caught my eye) but if you're after creating an actual cross platform application then unlike Qt, this one is free to use for both commerical and non-commerical use:
https://www.wxwidgets.org/about/

I'm guessing it might use 'widgets' along the same lines as the ones you are talking about

I was playing about with the idea of starting to learn it and rewriting my traffic simulator so that it was a standalone app that can import the data straight into different 3D apps.

Simon