Actually, I misunderstood you. They use hivemail for the free email service. I'm not sure if they use that for their mailing lists or if they use something else.
It could be accomplished via the use of a 'cronjob'.
Write a script to pull out the info. you want from your database, format it, then setup the 'mail()' headers for HTML content, put your formatted content into the 'mail()' message, and mail it to your members.
That is correct .. we use that one, with a few modifications to the template (changed colors and made it so all the bithdays, calendar envents, stats .. etc all have the same look as the posts)