Tiger also was the debut of Dashboard widgets, which opened up creating app-like experiences for those who knew HTML/JS/CSS instead of Cocoa (myself included).
To this day I miss being able to enter Dashboard with a single keypress like in the old days. I used that mini calculator, note taking app and weather widget constantly.
By I seem to be alone. For dome reason most people hated Dashboard.
Never mind the fact that apps like Calculator only allow a single instance/window for no reason. Only way around that is to literally duplicate the app!