A good, free, graphics package for mathematics?

A student of mine has cooked up a new graphical notation for computing with knots on surfaces. The trouble is, writing up his results is difficult due to his new notation. Is there a good "drawing tool" for mathematics that anyone can suggest?

Solution 1:

Asymptote.

Solution 2:

Inkscape is a good open source drawing package, and it integrates with LaTeX.

Solution 3:

I like to use the TikZ package in laTeX. It has a bit of a learning curve, but I like the fact that you don't have to call external graphics files when you compile the laTeX code. I used to use (and sometimes still use) Adobe Illustrator to create pdf files to incorporate into the tex code via an \includegraphics command.

Solution 4:

GeoGebra is nice tool that worth. I recomend using it.