PyVis - http://pyvis.sourceforge.net
Py/Tk based graphing library - totally cross-platform, requires only a standard distribution of Python
Intended both as an end-user graphing calculator, and a powerful graphing widget for use in your own Python/Tk programs.
It is provided under the MIT license, which basically means, do whatever you want with it
Download latest release of PyVis
Download latest release of Python (required to run PyVis)
Questions? Comments? write me an e-mail