A portable, multi-platform, command-line driven graphing utility
A famous scientific plotting package, features include 2D and 3D plotting, a huge number of output formats, interactive input or script-driven options, and a large set of scripted examples.
XPaint is a simple paint program for X, suitable for producing simple graphics. It does offer some advanced features such as image processing functions and gradient fill. XPaint was originally written by David Koblas.
SimBlob is a project to develop simulations that focus on interaction with the environment. Water flows, erodes the earth, alters river channels, forms lakes, and helps forests grow. Fires burn down forests. Volcanos reshape the landscape.