oregano : Oregano is an application for schematic capture and simulation of electrical circuits ( https://github.com/drahnr/oregano )
qucs : Quite Universal Circuit Simulator in Qt4 ( http://qucs.sourceforge.net/ )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a dev-zero
For Paludis use this rsync : rsync://gentoo.zugaina.org/dev-zero-portage
If you have a problem : ycarus(-at-)zugaina.org