GarageBand.com's complex technology ranks songs based on the community feedback.

FORBES: Podcasting Profits

Real-time 3D body motion data enables the development of apps that can recognize and classify complex motions such as sports techniques by digitizing your exact movements for immediate feedback and live sharing.

ENGADGET: Xsens teases wearable 3D body sensors that won't cost, will track an arm and a leg (video)

Complex systems such as climate and the financial markets have both positive and negative feedback.

FORBES: Chaos Theory, Financial Markets, and Global Weirding