Applets are small, single-purpose computer programs, usually available on the Web through a browser. For this site, I built the applets in GeoGebra, with the goal of making various mathematical ideas more visual and more interactive. However you cannot expect them to teach the concepts they illustrate! They are most effective if they are part of a multidimensional pedagogy that gets students to engage intellectually rather than watch passively.
You can use the applets online, and/or download the corresponding GeoGebra files and modify them to better fit your needs.
Some links below are to a single applet, others are to a launch page with links to several applets.
Changing a, b, c in `y=ax^2+bx+c`
Factored Form of a quadratic
Off and On, understanding linear inequalities
Stairs, slope puzzles
Doctor Dimension, exploring rate of change
Function Diagrams, a parallel axes representation
Iterating `f(x)=rx(1-x)` (in two representations)
Tri, Tri Again (inscribed circle iteration)
Pent, a two-person strategy game
Penumbra, some of the geometry of eclipses
Spirograph, exploring symmetric figures created by a circle in a circle
As I create more applets, I'll try to remember to add links in this directory.