Circuit schematic design
http://geda.seul.org/tools/gschem/
Printed circuit board design
Schematic capture (gschem) and circuit simulation (gnucap)
Gerber RS274-X file format viewer
Scientific data visualization
Raster graphics design
C compiler for couple of utilities written in C
Vector graphics design
http://sodipodi.sourceforge.net/
Raster image data processing
Keeping Ronja project source tree up2date
http://www.gnu.org/software/make/
Distributed revision control for the Ronja web
http://www.gnu.org/software/gnu-arch/
Ronja & Twibright Labs web scripting
Ronja & Twibright Labs web server
Text editor
Web browser (acquiring technical and scientific information from web)
PDF and PostScript viewer (viewing datasheets)
http://wino.physik.uni-mainz.de/~plass/gv/
Gallery image annotation and postprocessing
http://herrmanns-stern.de/software/mapivi/mapivi.shtml
Synchronization of image galleries
Vectorization of raster graphics
http://autotrace.sourceforge.net/
PCB processing scripts.
Operating system
Operating system kernel
Operating system
Order forms and database of parts
3D modelling
2D drafting