Students can draw graphs in a coordinate system. This program is good for especially high school students. The program makes it very easy to visualize a function and paste it into another program. Students can do calculations on the functions.
The National Library of Virtual Manipulatives is a library of uniquely interactive, web-based virtual manipulatives or concept tutorials, mostly in the form of Java applets, for mathematics instruction (K-12 emphasis). The project includes dissemination and extensive internal and external evaluation.