While I investigated applets from both WiseWeb and Illuminations, I discuss only ones from WiseWeb.

Two I liked:

I was impressed by Algebra Arrows and Shooting Balls. Algebra Arrows allows students to set up an equation using variables and then view a graph or data table. Students can easily manipulate the equations and instantly view the results on the graph. Although students could perform the same types of exploration on a graphing calculator, this applet set up the equations in a more natural way, allowing for better visualization of both the equation and the graphical results. I also found the graph itself easier to manipulate than with a graphing calculator, where you have to access menus in order to change the scale of the graph. This applet has a few limitations: first, it would be nice to be able to change the size of the graph, which I found somewhat limiting; and second, it had a limited number of operations available (e.g., it had no trigonometric operations, which would be nice for studying graphs of the identities.)

Shooting Balls allows the student to change the initial height (y-intercept) and slope of a line to try to shoot through several balls that are on the coordinate plane. Although I liked this activity, I believe that it would be best used as an introductory activity for exploring lines in the coordinate plane. Once students have a good knowledge of slope and y-intercept, the activity becomes more of a fun drill-and-practice activity rather than a visual exploration.

Two I didn't like:

Although I liked most of the activities on the WiseWeb site, some were less impressive than others. A few, such as Tic Tac Go and Guess the View, did not promote exploration of math topics, but were more just drill-and-practice activities. Tic Tac Go presents the student with a table that contains operations with integers. A number shows at the top of the table and students must match it in the table below. The student wins the game when he or she get three (or five) in a row. Although it is fun to play for a while, it is not particularly stimulating, nor does it help students visualize operations with integers.

Guess the view presents odd shaped 3D objects along with one view of the object (right side, top, etc.) and asks the student to identify which view is presented. The applet asks twenty such questions, and then gives the student a percentage mark at the end. Again, this applet only serves as a sophisticated drill-and-practice session. It doesn't use any techniques to provide any scaffolds for the student when the answer is incorrect.

References

Illuminations. National Council of Teachers of Mathematics. http://illuminations.nctm.org/

WiseWeb. Freudenthal Institute. http://www.fi.uu.nl/wiseweb/welcome_en.html