Right now, just one beta is available. It's called Explore and according to the site it allows users to find out what, "bloggers are saying right now on any topic, organized by how many links their posts are getting. Think of it as a newspaper front page for any subject."
In other words, posts organized by category. Remembering that this is a beta and lists posts by inbound links, I think I'm sticking with Topix.net's NewsRank algorithm and even the free version of NewsNow.co.uk for automated categorization of news and blog posts. Topix added blogs to their mix a few weeks.
Kudos to Sifry, Kennedy, and crew on the new site and a great name. We're looking forward to seeing what's next out of the oven and what improvements you make to Explore.