Xyce

[ScribblesOnNapkins]

I did not see a post about this so I figured I should throw up something. It is too interesting to ignore. The following quoted text is from their website.

"What is Xyce?
The Xyce Parallel Electronic Simulator is a SPICE-compatible circuit simulator, developed internally at Sandia National Laboratories and funded by the National Nuclear Security Administration's Advanced Simulation and Computing (ASC) Campaign. In continuous development since 1999, Xyce is designed to run on large-scale parallel computing platforms, though it also executes efficiently on a variety of architectures, including single processor workstations. As a mature platform for large-scale parallel circuit simulation, Xyce supports standard capabilities available from commercial simulators, in addition to a variety of devices and models specific to Sandia's needs."

https://xyce.sandia.gov/documentation/index.html

Using it in gEDA.
https://xyce.sandia.gov/downloads/_assets/documents/AppNote-GedaAndXyce.pdf

[ch_scr]

Not sure this section of the forum is the most appropriate? But now there is Spice in Kicad, so close enough I guess.
Having used XYCE a few times now (by means of Geda for schematic capture), I can report the following:
Compiling from source is a chore, getting the package needs registering on the website.
There are decent published guides on how to compile it, but it's not a short read and not all in one place.
The packages do come with some "proprietary device models" - maybe someone who has used them can shed some light?
I would hazard a guess they are good, coming from the XYCE people.
Using it is far from as-easy-as e.g. LTSpice. And by easy I mostly mean the round-trip of interactions to get:
schematic to netlist, netlist simulated, results plotted; adjust schematic or simulation command and go again.
The less clicks or console commands for that round trip, the more usable IMHO.
The only GUI supporting it is QUCS-S, and that project is slowly killed by being stuck in QT4-land.
Spicegui seems like an easy target to get at least some GUI action for XYCE, but I'm just a bloke running my mouth.
Also I'm not really happy with Spicegui on the whole roundtrip intraction-needed thing, TBH.
Mostly on the results plotting side of things; Gnuplot as in the xyce-Geda-howto works well enough...
What works really well, and is at least workable on the interaction side, is to make an XYCE simulation that spits out an s-parameter file, then use DeEmbed to plot the results. And that is something very usefull not many other (free) tools can do, a killer application if you must. Now if someone could make the "uncalibrated" data that shows up in DeEmbed every time you open a file disappear, that would brighten my day significantly. And maybe add a "refresh data" from changed file button (that keeps the other settings / views intact).
Ok, rant off 
TL;DR: XYCE is nice, using it: not so much.