PGF is a TeX macro package for generating graphics. It is platform- and format-independent and works together with the most important TeX backend drivers, including pdftex and dvips. It comes with a user-friedly syntax layer called TikZ.
xd3d is a simple scientific visualization tool designed to be easy to learn. It can plot 2d and 3d meshes, with shadowing, contour plots, vector fields, iso-contour (3d), as well as 3d surfaces z=f(x,y) defined by an algebraic expression or a cloud of points. It generates high quality vector PostScript files for scientific publications and still or animated bitmap images. It includes the graph plotter xgraphic.
PiX, a collection of batch utilities for GNU/Linux and similar platforms, creates mathematically accurate figures, plots, and movies using easy-to-learn syntax. The output is expressly suitable for use with LaTeX; figures may be written in a LaTeX picture environment containing PSTricks, tikz, or eepic macros, or as vector (EPS or PDF) image files.