Links ordered by topic
Numbers
Elementary geometry
Linear algebra
 Graphing Linear Equations
(applet) Learning program on linear functions and their graphical representation
as straight lines in a plane. Includes tutorial, test, quiz, crossword puzzle
and  as tools  the possibility to plot graphs of functions and a calculator.
You may pose questions to the teachers and discuss with pupils of the
Bremen High School, USA.

Graph Applet (applet) A straight line may interactively be moved, the
coefficients m and b of its equation are shown.
 Java Script Linear Algebra
(JavaScript) Some pages about how to manipulate
3 × 3 matrices (multiply, invert,...)
and systems of linear equations in 3 variables.
A particularly useful tool is the
Java Script Linear Algebra Calculator. On
page III
systems of equations may be solved numerically.
The same author also offers a
Matrix Calculator Applet
capable of dealing with
n × n
matrices, and a short outline of the
mathematics behind
(also see his maths pages).

Linear Equation Solver
(applet) Numerical Solution of systems of linear equations in
3 variables.
 HartMath
(applet) Symbolic manipulation with vectors and matrices in a
Java based online computer algebra system.
Vectors
Trigonometric functions and trigonometry
 Trigonometry (some applets)
A number of units to illustrate definitions, graphs and simple properties
of the trigonometric functions, including the
Sum Formulae, the Law of Sines and the Law of Cosines.
In particular see two applets about the graphs of the
Sine and the
Cosine function
and a further applet by which the definitions of the
various trigonometric functions may be compared.
Curves

Famous Curves (graphics and applets)
More than sixty famous plane curves or families of curves
are discussed and represented graphically.
In the applet versions their parameters may be changed interactively.
See also the
Famous Curves Applet Index. (School of Mathematical and Computational Sciences,
University of St Andrews, Scotland).

A Visual Dictionary of Special Plane Curves:
A lot of information on curves and families of curves.
Resources in various formats: images, Mathematica notebooks, Quick Time movies,
Sketchpad and Cabri files.
Integration
 Integration Applet (applet)
After typing in a function, the definite Integral is represented
graphically as area and its value is shown.
Probability and statistics
Numerical methods

Bisection Method Tutorial (applet)
Illustates the bisection method to numerically solve equations of the form
f(x)=0 for some selected functions f.
 Numerical Integration Tutorial (applet)
Some methods for numerical integration are applied to a number of selected functions and
illustrated graphically in a nice way.
Fractals
Fourier analysis
 Realtime
Fourier sound synthesis (spreadsheet) Sound generator:
Determine the intensities of overtones by means of a scroll bar and listen to the according sound.
(Even without sound utility, the graphical side of this spreadsheet is a nice
illustration of the Fourier series).
History of mathematics
And...
...last but not least: Mathematics as a problem
