All sites’ latest is a plugin for WordPress multisite installations to fetch and display latest posts from all sites of current blog’s owner, typically on the root site.
It is a nasty hack, but works for me (on WP 3.1.1) and doesn’t do any database writes, so testing it is quite safe. There’s no GUI for options, you need to edit the code if you want to exclude some sites for example. You’ll need to modify the code anyway, as you’ll have to set up a special page for displaying the fetched posts and point the plugin towards it.
Download Footnotes for WordPress (a .phps file, rename it to .php before uploading to plugins/)