GTKMathplot is an interactive plotting program based on GTK+ and the Cairo graphics library. It can display bidimensional curves, tridimensional curves, and surfaces from Cartesian or parametric equations describing the mathematical objects you would like to visualize. It is designed to be intuitive for high school students with good mathematical knowledge. University students of engineering, physics, mathematics, or natural sciences should need no explanation at all to start using it proficiently.
DeforaOS Phone is a GTK+ application that has an interchangeable telephony backend, complete with call, contact, and message management. With its backends for GSM modems, it can be used as the telephony application on phones including the Openmoko Freerunner, Nokia N900, and some HTC phones running custom Linux distributions, and as a tethering application that provides Internet access to a desktop computer. Support for VoIP protocols is under development, with a backend based on the sofia-sip library.