Shuriken - SqakAttack (Pc/Mac/Universal/Free)

SqakAttack is a midicontrolled buffersynth with a duck for GUI.

From the homepage:
Hook SqakAttack up with audio and midi then when you press a midi note whats currently coming in on audio will be used to synthetisize audio. Does it sound stupid and hard to grasp? check out my stupid explaination down under here with the video under the download links.

Price: FREE, but you can always donate.