I just tried QucsStudio. It has promise, but it still shows signs of opensource madness.
Well, I am not even sure if it is opensource. There are no links to the source that I could find, and it is not compatible with the Qucs project it is based on.
I tried the file based voltage sources - they could not read dat or cvs files. "No data" apparently. So either the feature is broken, or they have changed the format of both the dat and cvs files with absolutely no documentation, or even source code I can go to.
The Qucs file based voltage source example does not load (because of changes in the QucsStudio format), and even when you fix it so it can load, QucsStudio definitely reduces to understand the DA and CVS files.
So I will probably have to go back to the clunkier open source Qucs to do my tests. At least it works.
It is not a version of Spice, by the way - they explain why trying to base an opensource simulator on Spice is a problem. So it is not Spice netlist compatible, but they do have converters. The potential to combine analog simulation, VHDL compatible digital, S parameters, electric field simulation along with the mathematical power of packages like Octave is awesome, as long as they can end up with something that doesn't take 6 months to master.
Right now, it is good, but it does not come close to LTSpice for ease of use, documentation and graphics. The KiCad-based schematic interface is pretty good. Could even be a little better then LTSpice.