gEDA(OS: pc linux/mac OS ; Open source so could possibly be installed on other systems from source code)
gEDA is mostly oriented towards printed circuit board design which is used for electronic design released under the GPL.
gEDA is a collection of open source electronic design tools. They may be installed individually but by installing gEDA you get the lot.
gEDA is mostly oriented towards printed circuit board design (as opposed to integrated circuit design).
The ones most relevant to this discussion are:
*gschem schematic capture
*gsch2pcb transferes information from gschem to pcb
*pcb for layout
*gerbv-gerber viewer. Look at layouts
*wcalc-Transmission line and electromagnetic structure analysis
*Can produce other file types like ps and png.
* PCB is one of the most mature packages, being that it was started in 1990 on an Atari, and best free pcb tools out there. The application is feature rich, very easy to learn, has no limitations like Eagle, and blows doors over all the other packages listed here IMHO.Most importantly, PCB does include an auto-router!
* PCB, used in conjunction with gEDA schematic editor, is a great combination: easy to use, have huge libraries, large world-wide on-line communities, work cross-platform, and have professional industry support. Many Aerospace companies use the gEDA suite for example. Best of all, gEDA and PCB are open source and free to use. In addition, I think gEDA and PCB are even easier than Eagle to use as well.
As a consequence of the project's openness, schematic symbols, footprints, and utility scripts are freely created and shared amongst the members of the gEDA community at a spin-off website(gedasymbols.org)