As far as I’m aware, there’s not any actual effect creation software on the market. There are a number of programs to synthesize effects and noise, but creating, say, a gunshot from scratch takes a lot more work than you might think. Unlike photo and video, which are fairly easy to synthesize, audio has several factors to deal with, and it would take enormous creativity to create a unique sound that was even remotely similar to something real. And even the effect synthesizers out there actually use a real sampled sound and simply alter characteristics of it, they don’t create an all-new sound.
Your best bet is either to buy a SFX CD, or to make your own sound effects "the old fashioned way". Need a gunshot? Go to an indoor firing range and get the cleanest audio you can. Clapping and applause in a big hall? Lots of friends in your bathroom, baby!
There was a day not too long ago when sound effects were created "live" during radio shows and other programs. Research those a bit, and see what they used.
Ultimately, you’d be suprised what you can do to fool your brin into thinking one sound is another. Need footsteps through snow? How about stepping around a layer of corn flakes? And there are other examples. Figure out what you need, and figure out how to make it with what you’ve got. Ultimately, when you put a sound with a picture, if both are clean and clear, the human brain tries its very best to reconcile the two.
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