Here's free software for maths teachers and students which is really top stuff.
What is GeoGebra?
GeoGebra is a dynamic mathematics software for education in secondary schools that joins geometry, algebra and calculus.
On the one hand, GeoGebra is a dynamic geometry system. You can do constructions with points, vectors, segments, lines, conic sections as well as functions and change them dynamically afterwards.
On the other hand, equations and coordinates can be entered directly. Thus, GeoGebra has the ability to deal with variables for numbers, vectors and points, finds derivatives and integrals of functions and offers commands like Root or Extremum.
These two views are characteristic of GeoGebra: an expression in the algebra window corresponds to an object in the geometry window and vice versa."
So what does it actually do? It lets you construct elements listed in the quote which can be manipulated by the student. Not only can you manipulate the "geometry", but you can also see values of variables changing. Your construction can be exported to an applet embedded in a web page.
Rather than posting a screenshot, if you're in theis field, have a look at:
Home page: http://www.geogebra.org/cms/
Links to some examples: http://www.slu.edu/c...sses/maymk/GeoGebra/
See a webcast of these being constructed (instructions plus the final product): http://math247.jot.c...and%20Use%20GeoGebra
tony[edited to hyperlink links and add picture]