QCad is a powerful but easy to use 2D CAD program for Linux, Windows, and Mac OS X. It uses DXF as its standard file format. While other CAD packages are often rather complicated to use, QCad tries to stay comfortable, and even an absolute beginner can create professional drawings with a minimum of effort.
PLOTICUS is a command line utility for creating bar, line, pie, boxplot, scatterplot, sweep, heatmap, vector, timeline, Venn diagrams, and other types of charts and plots. ploticus is good for automated or just-in-time graph generation. It handles date, time, and categorical data nicely, and has some basic statistical capabilities. It can output to GIF, PNG, SVG, SWF, JPEG, PostScript, EPS, and X11. You can use convenient preset options or create complex scripts with rich and detailed color and style operations.
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. The distribution includes the graph plotter, xgraphic.