SPICE was developed under, is and always has been UNIX based with most instances of the software also being actively run under Unix. There are very few windows variants in comparison. As a result there is a many different flavors of spice out there and many that are FOSS. gEDA, XSpice etc. A quick search under EDA on freecode (the old Fresh meat repository) shows 16 instances, but not all are free. Another search under source forge shows GNUspice and ngSpice.
There is even a FEL spin (Fedora Electronics Lab) that is slightly out of date and has many, many EDA tools bundled into one focused version.
As far as I know, there isn't something like Proteus for Linux.
If you don't mind using Wine to run Windows applications in Linux and using a closed-source application, LTspice runs perfectly there (this is what I use, usually)
Otherwise, there's ngspice, for which Oli already has pointed to an ngspice GUI.
Sorry.I can't post the article one time.
I am blank.