Back in 1999 a group of Microsoft employees comprised of Seamus Blackley, Ted Hase, Otto Berkes, and Kevin Bachus began work on a “Windows Entertainment platform” with the hope to see Microsoft release a gaming console to rival Sony’s Playstation 2 by leveraging the company's’ DirectX technology. These friends would label the project “DirectX Box” after said technology and a year after the idea had first started to come together it was officially unveiled as the Xbox, “the future of console gaming” which would eventually release on November 15th 2001.
*As voted by NeoGAF.
*As of the 6th generation. Titles exclusive from 2001 - 2005
I'll be adding to this as I see them.