Difference between analog simulator and digital simulator?

The big difference is inputs and outputs. Digital ICs expect high/low true/false inputs and outputs. Analog ICs take any inputs, and produce outputs of any level. For example, an audio amplifier is an analog IC. It takes an analog input (sound), and produces an analog output (louder sound). A ripple counter is an example of a digital IC. It takes a digital input (clock pulses), and produces a number of digital outputs (the digital outputs of the flip flops, collectively representing a number in binary).