It seems that no one actually announced the creation of the "newprojects" mailing list yet!
The mailing list[1] is an announcement-only list for new Wikimedia wikis[2]. The way it works is that the addwiki.php[3] script that sysadmins use to create the wikis automatically sends a mail to the list, so (provided there are no bugs with the script) subscribers will get an e-mail when every Wikimedia wiki is created.
This list should be especially useful for people who need to know when new wikis are created so that they can update their tools or scripts. Of course, people who are just interested in knowing about new wikis are welcomed to subscribe too. :-)
[1]https://lists.wikimedia.org/mailman/listinfo/newprojects [2]http://meta.wikimedia.org/wiki/Special:SiteMatrix [3]http://wikitech.wikimedia.org/view/Add_a_wiki