ofxSuperInterface is an openSource GUI for openFrameworks, working on both desktop/iOs application.
Note : It's still very beta! 

Working with a grid system + xml file.
Interface is liquid, you can dynamically change the position of the components and scale them.
Also can send OSC information.

Dependencies : 

ofxXmlSettings
ofxTween

ofxOsc is needed if you want to enable OSC communication by adding #define USE_OSC in superInterfaceDataManager.h

Basic use : 

superInterface.setup();
//superInterface.setup(ofxiPhoneGetDocumentsDirectory()); if you're using iOS

Then declare your components i.e. : 

slider.setup(&superInterface, &app->pct, 20, 20, 10, 2, 0.0, 1.0, "Glitch Intensity");

add it to the GUI, choose which page

superInterface.addComponent(&slider, 0);

Then you can change positions in the settings menu, also the global size of the components

See the example for more info ( listeners, components, OSC, etc.. )
Don't forget to add the font in your data folder!