Is there an C++ API for GUI development that is open source and cross platform (kinda like Java Swing, but in C++)

: Is there an C++ API for GUI development that is open source and cross platform (kinda like Java Swing, but in C++)
:

None that I am aware of -- I've seen several that cost $$$, and one that can be used free for learning purposes, but costs $$$ if you want to sell the product. .NET is heading that direction, but its certainly not free (except there are no royalties for the product(s) produced by the Vusla Studio .NET)

: Is there an C++ API for GUI development that is open source and cross platform (kinda like Java Swing, but in C++)
:
There are 2 that I am aware of:

QT- it has a free, open source version, but forces you to open source your code if you want to release the program. Otherwise it is stupidly expensive, but is cross platform.

wxWidgets- Open source, cross-platform, and free. You can do whatever you want with the resulting programs you write.

Both are more then a GUI library, they have string classes, network libraries and more. There are parts of C++ that are not directly supported in either, but you can use anything in C++ along with the above libraries.