I need an advanced subscription system with custom delivery policy for each user

[ Moderator note: moved to How-to and Troubleshooting. ]

Hi
I like WordPress very much because it gives each user the option to customize their own preferences, but I believe WordPress still lacks a real customizable subscription system. I would like to have a subscription system with the following possibilities:
1- Customizable Subscription: Each user has the option to subscribe in their desired post (comments(, desired categories or desired page (comments).
2- Alert System: Each user is able to subscribe to their desired post content. For example someone selects: alert me whenever a post contains one of the following phrases:
computer, technology, mobile application, software
3- Customizable Delivery: Each user can select how they would like to receive notifications about the subscribed items: monthly digest, weekly digest, daily digest, immediate notification, no-email notification. “No-email notification” means, not receiving any email, but reading all the updates of subscribed categories and posts in the subscriptions page (like VBulletin and PunBB).

Also, Customizable Throttle feature is of course a must-have for every subscription and notification system, so the admin can adjust the numbers of emails sent per hour.

Thank you