Ngspice project aims to improve the spice3f5 circuit simulator.
Ngspice running on Windows XP within Cygwin
ngspice on KDE (Linux)
ngspice on KDE (Linux) with gschem in background
ngspice on Sun-Solaris compiled with gcc
ngspice running on MacOSX (nedit is the external editor)
ngspice running on Windows XP compiled with MinGW