Manipula Math with Java is a Japanese website that has an excellent collection of Java applets that can be used for teaching and learning mathematics. There are 279 applet collections divided into the following categories: Middle School, Trigonometry, Vector, Calculus, Complex Numbers and Conics.
Euclidâs Elements is the most successful and influential textbook ever written. Only the Bible has been published in greater number.
Amazingly a Professor of Mathematics at Clark University has translated all thirteen books of Elements and made them available online. This would be fantastic in itself but the icing on the cake is that there is an interactive geometry applet to support each postulate so you can literally interact with the maths!