BRL-CAD is a powerful constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing support for rendering and geometric analysis, path-tracing for realistic image synthesis, network distributed framebuffer support, and image and signal-processing tools.
The GOBLIN project consists of a C++ class library for a large series of graph optimization problems, GOSH, an extension of the Tcl/Tk scripting language to graph objects, and GOBLET, a graphical user interface to the library functions. GOBLET includes a graph editor and supports the standard graph layout methods.
GPSBabel converts waypoint data between about fifty file formats, including Magellan and Garmin serial, Garmin USB, Mapsource, Mapsend, Streets & Trips, Delorme, National Geographic, many PDA formats, and many others. It is endian and word-size safe, includes a GUI, and runs on a variety of operating systems. It also supports Groundspeak GPX extensions for geocaching.
OMNeT++ is a C++-based object-oriented Discrete Event Simulation framework, primarily targeted at the simulation of communication networks and other parallel/distributed systems. It includes a graphical network editor, a network topology description language, a rich simulation class library, multiple execution environments (both GUI and command line), a result plotting tool, detailed documentation, many sample simulations, and much more.
PLplot is a library of C functions that are useful for making scientific plots from programs written in a wide variety of languages. It can be used to create standard x-y plots, semi-log plots, log-log plots, contour plots, 3D plots, shade (gray-scale and color) plots, mesh plots, bar charts, and pie charts. Multiple graphs may be placed on a single page with multiple lines in each graph. Different line styles, widths, and colors are supported. A virtually infinite number of distinct area fill patterns may be used. A variety of output devices and file formats are supported.