For an excellently written, detailed, tutorial-style introduction to the Open Inventor API used by the Coin library, we highly recommend the book «The Inventor Mentor» (subtitle: «Programming Object-Oriented 3D Graphics with Open Inventor»), ISBN 0-201-62495-8. It walks the Coin application programmer through all the principles applied in the API, richly illustrated and with numerous, well documented code examples.
(The «The Inventor Mentor» is getting a bit old, but don't let that put you off. We heartily recommend this book as it covers all the principles, aswell as close to 100% of the API, in an excellent manner.)
Systems in Motion is working on providing libraries for interfacing Coin with a wide range of windowing systems and GUI toolkits.
See <http://www.coin3d.org/> for more information about Coin and the GUI toolkit libraries.
IMPORTANT NOTE: the online documentation for the Coin library is still a work-in-progress. Although most classes have been documented properly, there are still a few "holes" in the documentation for certain classes. If you happen upon an undocumented or poorly documented class and / or class method which you find hard to understand, please give us a notice so we can rectify the situation.