I am looking for a third party program...

I am becoming more and more interested in mashups. If you don't know what I mean, a mashup is a collaboration of multiple songs together, to make a cool sounding song. If you want an amazing example of what I mean, Go on Youtube, and look up " Girl Talk". I know he uses a PC, but I am wondering if there happens to be a program, that would be just as good for macs, that I could create my own with?
Any help, Thank you.
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