Tiger ushered in many new features that we all love to use (and some of us love to hate). Apple says there are over 200 new features in Tiger, though most aren't as big as your Dashboards or your Spotlights.
launchd is one of those smaller features that might be overlooked by most users, but Apple's Developer Connection has an article up detailing all the cool things it can do. What is launchd? According to the article it is, 'a new system startup program,' which allows you to, well launch stuff on a schedule.
If you want to learn more about launchd, read the article.