SoGtk is a C++ GUI toolkit for using Coin with GTK+. It can also be used on top of Open Inventor from SGI and TGS. The API is based on the InventorXt API originally from SGI.
GTK+ is a multi-platform toolkit written in the C programming language for creating graphical user interfaces. So far it works with the X Window System, with several ports under way.
For more information on the GTK+ toolkit, see the project's web site at <http://www.gtk.org>.
The corresponding documentation for Coin is located here.