This software is the best.

KiCad EDA

Here is a link to the website, hope it helps.

http://kicad-pcb.org/

kicad is a PCB tool. completely unrelated.

you can try free versions of spice, at least that will give you the ability to simulate tunnel effects if you have a model for it. there are free models out there.

ngspice , microwind, Xcircuit

Here's a set of free tools, including schematic capture, simulation, DSP and model generation

http://www.designsim.com.au/analog.html

which run on Linux or Sun SPARC