PLplot is a cross-platform, scientific graphics plotting library that supports math symbols and human languages (via UTF-8 user input strings); plot capabilities for multiple non-interactive plot file formats and in multiple interactive environments; and bindings for multiple computer languages.
tkBacktracer is a cross-platform interactive visualization tool to explore the tool motions in RS-274D "G-code" CNC files used in computer controlled milling and manufacturing.
MSDViewer (My Schematic Drawer and Viewer) is a schema editor using a simple text file as input. Requires tcl/tk (>8.4) and Iwidgets (>4). should work on every platform supported by tcl/tk. Output postscripts.