Innovation
Igor Bazdyrev asks, "Does OS X make developers more innovative?", citing Clutter and Tinderbox.
The best feature of Tinderbox is Tinderbox's agents automatically scan your notes, looking for patterns and building relationships. Agents help discover relationships and help make sure important things don't get lost. Agents are easy to make and easy to modify. They're flexible and powerful.
I don't think the operating system makes developers innovative. But the Macintosh side of the world tends to be livelier for software developers right now. People tend to buy Macs with their own money, while many of the Wintel boxes are purchased with other people's money. People who invest in exciting new computers are perhaps a little more likely to invest in exciting new software.