SPICE Programs worth learning for
Many large semiconductor companies have in-house developed and enhanced versions of SPICE -- e.g. see in-house SPICE. These typically support the more complex needs of high performance and high volume IC designs. Other companies frequently just use the simulator that comes with their EDA tools.

Enhancements to SPICE might include support for specialized device models, significantly higher speed and new algorithms for convergence, large circuits or new simulation options.