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?
 A: Asymptote.
A: Inkscape is a good open source drawing package, and it integrates with LaTeX.
A: 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. 
A: GeoGebra is nice tool that worth. I recomend using it.
A: On unix or Mac environments try xfig. There are windows simulators. Picture environments can be used with LaTeX to draw, but they are a pain (we used this in "The Classical and Quantum 6j symbols"). We used xfig for both "Knotted Surfaces and Their Diagrams" and "Surfaces in 4-Space." Otherwise, get a good set of Rapidograph pens, some blue pencil, and lots of white-out. 
A: LaTeX is a good way to write all mathematical formulas and graphical notations.
It is a lot more than that, but personnaly, I use it frequently only for that.
A: There is also something called as TeXmacs which you might be interested in. As Xavier quote LaTeX is the best way to start. 
In case you are in need of a drawing package i list the following 3 packages which are commonly used:


*

*pstricks

*PgfTikZ

*Gnuplot
Please google the names and you shall find lot of interesting things.
A: I often use both LaTeX and GeoGebra. They are my favourites these days...
