Assuming you are talking about 'Electronic Circuitry' when you say 'Simulation'....
There has been MASSIVE movement in this field over the last 2, 5, 8 years.....
The MAIN original 'contender' is the "SPICE" that you mention. Meaning....
"Simulation Program with Integrated Circuit Emphasis".
Virtually every other similar system is today BASED on this, but with various
new front-ends. Be it Graphically, or real time functionality !
The 'Branch' of such a Forum would be huge ! due to this great diversity !!
Let's outline the 'basics' of this topic, so others can understand too.
Electronic enthusiasts would find it great to 'Simulate' an Electronic Circuit before
having to actually 'build' it. That's a 'given' xx. SOME software does that fairly
well, but has many limitations. 'Some' of them allow you to run a 'sequence' which
results in charts/graphs of voltage/current in parts of the 'circuit' to analyze.........
However, the best of the best is "Circuit Wizard" which continuously runs in REAL
time, and allowing real time intervention with many component values. It pretty
much includes every type of general transistor/diode/ic that you will generally use,
and can choose many types of outputs/inputs, including REAL loads etc.
On top of that, when you are happy with your 'Circuit', it takes into account ALL
the dimensions/pinouts of components, and auto-designs both single & double
sided PCB's for you, with auto component arrangement, ready for printing....