What are the GUI libraries used by Unity3d and other software that doesn't look like traditional applications?

I have been dealing with GTK & QT on linux, Windows forms on windows and some others like Tk, Wx. But I can see a lot of GUIs that don't look like traditional applications like unity 3d, some Adobe开发者_C百科 applications, 3ds max etc..

Are they using special libraries ? or there is a way for advanced theming of the above libraries ? Or are they just creating their own libraries ? How do they create them ?

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Well usually they make their own libraries

Some applications ( exp : Blender ( that has a really good GUI )) use there own libraries .

Blender implements its whole GUI using OpenGL so Unity , 3DsMax should be similar

*By ( that has a really good GUI ) I mean it looks good

*3 years but I Just saw the question ;)

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A lot of the libraries that are independent will do a lot from scratch. Eg. use Cairo directly in building their engine so that they can do display and capture input from the users as well. A lot of the widgets they have for the GUI are done from basic bottom up principles. The new non-server standalone apps can use frameworks like Electron (which desktop apps like Skype now use) rely on HTML/CSS/Javascript so that the primitive widgets are the standard browser elements of a webpage navigation in an application form.