In 1999, Bungie was probably the best-known studio developing specifically for Macintosh, having delivered titles like Marathon, Myth, and Pathways Into Darkness. At Macworld 1999, Steve Jobs introduced the studio's next big Mac exclusive: Halo.
Within a year, Bungie would be bought out by Microsoft and Halo would become a launch title that, more than any other game, made the Xbox viable in its infancy. Although Jobs had sworn that Apple had "put an initiative in place to get games back to the Mac," the new console project and Microsoft's commitment to it seemed a much more stable environment than remaining the lone standard bearer of gaming on the Mac.
People argue the Halo franchise's innovation and significance, or lack thereof, all the time. What isn't disputable is its place in history to these two companies, as the catalyst for the fortunes of one and the persistent listlessness of another, at least in gaming. I often wonder if Macintosh really could have evolved into a serious gaming platform, using OpenGL, with Halo as a leadership title. And I wonder what would have happened with the Xbox - if anything could have matched the impact of Halo on that console, or if Microsoft would have simply developed another multiplayer FPS with which to stake its claim in the market.
Above is Steve Jobs' keynote introduction of Halo on July 21, 1999 at Macworld Expo in New York. The game had been given a closed-door screening at E3 earlier that year. This is its public debut.
Eventually, Halo would make it to the Mac. In 2003.
Halo ... On the Mac? [YouTube]