[jcelerier]

There's also Qt which they used for OneDrive

[pknopf]

Yup, and you don't even need to touch C++ these days. All C# and QML!

https://github.com/qmlnet/qmlnet

(I'm the author)

[tinus_hn]

I’m not sure if it’s true but it seems to me like they replaced their own client with an alternative one they bought from another company, which has parts written in Qt.