Slope is a free (LGPL) C library for data visualization. It integrates with Gtk+ and all the drawing is made with cairo, so it doesn't depend on nothing outside Gtk.
Our goal is producing beautiful, publication quality, and fast charts from numerical data. We are in part inspired by Python's matplotlib and the browser's mighty D3.js, but commited with the raw speed of C programs. We beleave Slope together with the GNU Scientific Library (GSL) is the best replacement for the set (NumPy, SciPy, matplotlib) in C's world.
If you want to try, just download or close the repository and use CMake to build (yes, we would appreciate if some one contribute automake scripts).
If you want to contribute to Slope feel free to issue a pull request or sugest something directly to me at email@example.com