Subscription
This is a new generation Subscription module that combines the functionality of the existing Subscriptions and Notify modules. The module enables users to subscribe to be notified of new contents on a site. Notifications can be by email, by the watchdog page, or by sms (text message).
The module enables you to combine subscription rules in complex ways, so
that, for instance, you could subscribe to only one user's blog. This is
more flexible than in the previous modules.
It is easy for other Drupal modules to generate notifications that can
then be distributed by the subscription module. Currently, the following
major module types [story, blog post, book page, event ... etc. ] can all
be part of a subscription.
(Lastest CVS wersion work with Drupal 4.7, use DRUPAL-4-6 CVS branch with Drupal 4.6x)