Grace is a WYSIWYG 2D plotting tool for the X Window System and M*tif.
Jmol is a viewer for chemical structure data.
Lynx is a text based web browser.
Maestro is a graphic interface for Jaguar.
Ploticus is a free GPL software utility that can produce various types of plots and graphs.
PyMOL is an OpenGL based molecular visualization system
Smokeview (SMV) is a visualization program used to display the output of FDS and CFAST simulations.
surf is a tool to visualize algebraic curves and algebraic surfaces.