These are tools we actively develop and maintain to make your application development easier.

GTK+

GTK+ is a free, easy to use, cross-platform toolkit. It is used for VMWare Workstation, GIMP and the GNOME Desktop among others. It is the corner stone for the interfaces used on the One Laptop Per Child computer, The Nokia N-series Internet Tablets and the OpenMoko mobile phone.
GTK+ Website

Devhelp

Devhelp is a is a tool for browsing and searching the API reference documentation for the GTK+ platform. It can be used as a integrated part of the Anjuta IDE and the Glade interface designer. It can also be used for browsing the documentation for your own libraries and applications.
Devhelp Website

GLib

GLib, a low-level core library that forms the basis of GTK+. It provides data structure handling for C, portability wrappers and interfaces for such run-time functionality as an event loop, threads, dynamic loading and an object system.