KLIC does analog IC design with SmartSpice Version 2.24.8.R from Silvaco of of Santa Clara, CA. This program started out as an HSPICE clone - and how that came about is amusing, but you'll have to look elsewhere for the story.
Modern MOS processes use binned BSIM models, with lots of parameters added to the basic Berkeley BSIM model by the simulator vendor. The "gold standard" is the HSPICE model, and the Silvaco model comes very close to that (one or two parameters renamed, and different numbers for model levels). Similar models are available in the Cadence simulators, and perhaps other simulators as well. Unfortunately, there are no open-source models that are clones of this family of vendor models.
Given that Silvaco does most of the process modelling for the big custom fabs, it is not surprising that their models fit the processes very well. And a bad model can lead to design failures, extra mask cost, and delay. So, if you want to play with the big boys, you have to run the simulators the big boys use in order to run their models. Silvaco is less expensive, and in my opinion a more capable simulator than current versions of HSPICE. Though it is closed-source, it is available for Linux, Solaris, and Windows. The Linux version is, of course, the best.
You don't have to purchase a full license for SmartSpice. If your needs are modest, or you just want to learn about the tool, you can download a special version of SmartSpice and manuals from eecad, and purchase runtime over the web. For short runs, this is OK, but if you are frequently running big multi-hour simulations, or if you want access to Silvaco's excellent tech support (Hi, Colin!), it is better to buy a permanent license.
I run SmartSpice with a parallel-port license key, the HASP from an Israeli company, Aladdin. Although Silvaco provides dongle drivers with their CDs and for download, it is better to go straight to Alladin for the most up-to-date versions for new Linux kernels. Look in Support/Downloads.