As far as I am aware Qt is the only cross-platform toolkit that has reasonable traction, and it has been successfully used by commercial applications. Other cro

As far as I am aware Qt is the only cross-platform toolkit that has reasonable traction, and it has been successfully used by commercial applications. Other cross-platform applications are either so old that there was no other choice but to write their own toolkits, or they are web browsers where you might as well write your own toolkit since you already have to do much of the work to render the HTML. Unfortunately, "well-integrated" and "cross-platform" are fairly mutually exclusive, kind of by definition. I'm not sure if the API model for Windows and macOS even have a generalizeable common model. (They might, they might not, I've not investigated, and it would depend on which of the many MS UI APIs you are using)