Quite Universal Circuit Simulator(QUCS) is a open source SPICE based circuit simulator. It is available for download at: http://qucs.sourceforge.net/
It is a nice alternative to ngspice for those of us that insists on using free(libre) software, but who would rather have a GUI for drawing our schematics.
This article will not be a extensive walk-through of the capabilities of QUCS, I just wanted to let the readers of our blog know about it's existence. Please refer to the documentation for more details.
DC-simulation of a simple voltage divider.
DC simulation including annontation of the currents
The output characteristics of the transistor obtained by using a dual parameter sweep.
Output characteristics of low-pass filter obtained by AC frequency sweep.