Eva, who is great at finding these sorts of things, has sent me a couple of links to follow.
The first one is Magnolia. No, this is not a site for the neighborhood with great views on the bluff overlooking Puget Sound. Magnolia is another social bookmarking site, enabling users to share websites, form groups, and carry on discussions. It was easy to set up an account, add a bookmark, and tag it with key words so other users can find the bookmark using the search engine.
The next is edu 2.0. It's a new free, web-based learning management system. This looks like it's primarily focused on K-12, but seems simple and easy to use.