[tomcam]

JUCE is a very, very well-designed cross platform framework that was used very successfully in the development of Tracktion, a competitor with programs like ProTools and Garageband. The API is C++ based but carefully designed to shield you from the weirdness of C++; if you needed to create a cross platform app and learn C++ at the same time this would be the gentlest possible introduction.

Jules, the creator and prime maintainer of JUCE, is indefatigable. I think maybe he's triplets, but nice triplets. He answers questions on the forum (http://www.juce.com/forum) at all hours and with extreme patience. There seems to be absolutely no difference between the way he treats casual users vs. enterprise customers on the forum.

JUCE can be used to develop audio plugins, synthesizer programs, etc., but is also a complete framework for GUI apps that have nothing to do with audio. It has canvas drawing, 3D support, and forms support.

There's a ton of documentation on the site and the source code is a dream to read. If you were creating an API for something you would be well served to see how Jules did it.

I rank JUCE with web2py as one of the two most comprehensive, ridiculously underrated open source products I've encountered.

[GuiA]

Max/MSP, one of the more popular visual programming languages out there, is also written using JUCE.

https://cycling74.com/forums/topic.php?id=11656

[lobster_johnson]

Does it use any native controls, so that you can build an app that looks and feels native? Could you build, say, something like the Spotify desktop app with it?