For Electronics Design there is Kicad(http://www.kicad-pcb.org/) and the GEDA(http://www.geda-project.org/) as open source solutions.
I would prefer KiCad as it is more user friendly than GEDA. But both lack a lot compared to Altium Designer. But they are open source so that lacking can (theoretically) be cured by enougth people using it,..