10. Halo: Combat Evolved
Development begun: mid '90s
Halo was originally slated for a dual release on Mac and PC. Bungie had previously worked in Mac development on their Marathon series, a precursor to Halo and a great trilogy in its own right. In addition, Halo was conceived and developed as a real-time strategy game, though it eventually became the benchmark first person shooter loved by millions today.
The best part of this story? The irony of Steve Jobs at the Macworld Conference and Expo in 1998 announcing that Halo would be released on Mac and PC simultaneously. Needless to say, this didn't occur, and Halo wound up putting millions of dollars right into the deep, deep pockets of Jobs's biggest rival, Billy Gates. Though that didn't come to pass without a few years of delays and redesigns, of course.