Google is your friend....

http://en.wikipedia.org/wiki/LTspice

....there's plenty to read in the links there.

I've already read it. Just want to know key difference of linear and non-linear possibilities in this software.

You are a fast reader, but you may have read too much into the statement than intended. Where did you read that it was "...for simulation of Linear circuits only...", and how did you come to your conclusion regarding "non-Linear"?

Hint: What is the name of the company whose chip models are included in LTspice?

Linear Technology spice = LTspice. I didn't tried the software much but wish to know how it is different from simulation softwares like multisim,circuit maker etc.