This plugin automatically takes your oldest post, and updates its timestamp so that it appears as the latest post on your WordPress site. It does this by utilizing the cron feature built into WordPress 2.1. It can rotate all the posts on your site, or just ones in a specific category. You can currently schedule it by setting the number of hours between shifts. For example, set it to 24 hours and it will shift the oldest post every day, at the time that you enabled it.
Scheduled Post Shift, WordPress, Plugins, WordPress Plugin