We have just started the pre release testing & community feedback for our J!Mail alerts project & its now in Labs..

Here's what it is in short :

1. A Mail alerts extension that allows users to set update preferences : Weekly/Fortnightly/Monthly .
2. Supports a plugin architecture to allow any extension developer to make plugins for his own extension updates.
3. What we plan to ship it with :

JomSocial

a. JS Latest Groups -
b. JS Latest Photos -
c. JS Latest Videos-
d. JS Latest Users
e. JS Pending Connections -

CB

a. CB Latest Users
b. CB Pending Connections


Other Extensions

Remository Latest Docs
Joomla Latest News
Latest SOBI Listings
Latest Virtuemart Products
Latest My Blog Blogs

Here is where you can see some screenshots & add comments & feedback.
techjoomla.com/techjoomla-labs/mail-alerts-for-joomla-cb-a-jomsocial.html