Has anyone developed a tool for sending automated email reminders to users after six months to tell them to update their page before it automatically unpublishes?

We're looking for a user management tool or page expiry system, either commercial or something you've developed for your own use that could be adapted.

Specifically we're looking for:

1. Better permissions management for groups and individuals, including the ability to easily grant permissions on a page level
2. A workflow or tool that expires content that hasn't been updated in a specific time period, after the user has been sent reminders to update their pages

If you've got any recommendations, please let me know. Thank you. Jane