Power Mac G4 Cube

The power (it had a PowerPC G4 processor) of three (a cube) and four (G4) wasn’t quite 8 x 8 x 8 (although sometimes claimed to have those dimensions in inches, it was actually 9.8 x 7.7 x 7.7 inches).

Twentieth Anniversary Macintosh

A year late (it was released in June 1997, for Apple’s anniversary on 1 April 1996) for a limited edition (it was possibly the only such Mac) that was cut to 20% in under 10 months (final stocks were sold off in March 1998 at a price of $1,999, compared to the original price of nearly $10,000).

Macintosh Portable

Despite its choice of trackball or keypad (introduced in September 1989, its trackball could be swapped out for a numeric keypad), it weighed more than some desktops (it weighed 15.8 lbs, heavier than a Mac IIcx, IIsi or LC series).

These were each novel designs that failed to sell as well as had been expected.