Windup Radio... but no Mac
One of the more interesting old rumors was the "Wind-up" portable computer based on a technology first applied to a radio.
This March 1999 Wired article discusses the technology and Apple's interest:
Stear confirmed that Apple Computer has been talking with his Capetown-based company about using the technology in future Macintosh products. But don't expect a windup PowerBook this spring -- the generator is still in development, and Stear said the companies have not inked a deal.
The windup battery seems to have hit the mainstream... not in a computer, though - but the original wind-up (& solar) radio is now on sale at JC Penny... $39.99. And - they come in translucent iMac-like colors. :)