Is it possible to simulate transistors using open-source tools only?

How fast are the available solvers?

How hard is it to interface with existing PDKs?

The following talks provide very promising answers:

* ngspice - an open source mixed signal circuit simulator, by Holger Vogt
https://peertube.f-si.org/videos/watch/62e7ad36-e7fc-4884-971a-9fcedf17d9f2

* Gnu Circuit Analysis Package (GnuCap), by Al Davis
https://peertube.f-si.org/videos/watch/5cae10a1-c5c6-45d3-9ade-949c0d3a2062

* Converting 45nm transistor netlists to open standards, by Thomas Benz
https://peertube.f-si.org/videos/watch/40e29b80-8a91-445c-b3cc-1fb886d7d51b