GMT is a free collection of UNIX tools that allow users to manipulate
(x,y) and (x,y,z) data sets (including filtering, trend fitting,
gridding, projecting, etc.) and produce Encapsulated PostScript File
(EPS) illustrations ranging from simple x-y plots through contour maps
to artificially illuminated surfaces and 3-D perspective views in black
and white, gray tone, hachure patterns, and 24-bit color. GMT supports
25 common map projections plus linear, log, and power scaling, and
comes with support data such as coastlines, rivers, and political
boundaries.

The package also includes supplemental programs, html documentation,
and examples.

Homepage:
http://gmt.soest.hawaii.edu/
