Windows Vista
Mac OS X
Sega Dreamcast
Team Fortress 2
 
Correct Answer: Sega Dreamcast

A brief explanation why…

Team Fortress 2: First shown at E3 1999, TF2 was repeatedly delayed as Valve transitioned from making games on the GoldSrc engine to the Source engine. The title finally launched in October 2007 with many differences over its original demo, including cartoon graphics instead of a modern war theme.

Windows Vista: After being delayed multiple times, many began to wonder whether Vista would actually debut, and although it may have been used prematurely and partially in jest, vaporware was commonly used to describe the operating system before it eventually launched in January 2007.

Mac OS X: "Winner" of Wired's 'Vaporware 2000' award, OS X was first announced in 1998 and faced several setbacks during its development, leaving many to question whether it would ever arrive -- it finally did in March 2001.

Sega Dreamcast: While it may have been vaporized by the PlayStation 2, the Sega Dreamcast was never considered to be vaporware, having been announced as the Sega Katana in 1997 and shipped as the Dreamcast a little over a year later (1998 in Japan, 1999 in North America).