GeoGebra is a complex mathematical application for those that study or work with arithmetic, geometry, algebra and calculus.
Aimed at math experts
It's a rather complex application that's aimed strictly at those comfortable with difficult math, but the advantage GeoGebra offers over similar apps is that it provides multiple representations of objects that are all dynamically linked. The idea is to connect geometric, algebraic, and numeric representations in an interactive way. This can be done with points, vectors, lines, and conic sections.
GeoGebra allows you to directly enter and manipulate equations and coordinates, enabling you to plot functions; work with sliders to investigate parameters; find symbolic derivatives; and use powerful commands like Root or Sequence.
The complexity of the program is mind boggling for those new to such mathematical applications. It's very difficult to work out how to use from scratch, although there are several very detailed tutorials to help you on your way.
Not for the faint hearted
GeoGebra isn't a mathematical program for the faint hearted but if you have to deal with arithmetic, geometry, algebra and calculus on a regular basis, it is very flexible.
The latest version of GeoGebra includes tangent to Freehand Functions, as well as the ability to save projections for 3D view (unless "Gray-scale" and "Omit green channel"), a "Use Lighting" option for 3D view (turns off shadows), and a "Show All Objects" button for 3D view.