I hope this will be of interest to some of you. I am working on an open source maths project called Sympl (www.sympl.org).
This is a cross platform tool for creating interactive graphs of various types. It can run on the desktop, but it also has an applet version, so you can easily integrate the graphs into your Moodle pages.
These can be static graphs (with pan, zoom and measure tools), or interactive graphs with control points which users can drag around. Graphs are controlled by simple scripts which give very flexible control. There are some example scripts on the website which can be used as-is or adapted for other purposes.
It is early days, but I would appreciate any comments or suggestions for new features. Please also consider copying any comments to the Sympl forums (http://www.sympl.org/forum), where other Sympl users can read them.