Marcus Campbell has released Scuttle, an open source bookmark manager (think del.icio.us, but hosted on your server), built on PHP and MySQL and released as open-source under the GPL. I'm interested in this because I have been looking for a method for my 4th and 5th grade students to catalog and organize their web resources on the building network. While tools such as Furl and del.icio.us are interesting, the one thing that has held me back from using these with my students is the whole aspect of requiring them to register with a third party. By running a tool such as Scuttle (or the also recently released de.lirio.us) we can take advantage of a social bookmarking tool, but keep it on our local network.
Another interesting aspect of this is using a tool such as Scuttle with the Live Bookmarks feature of Firefox. Let's say that some 4th grade students are researching a topic. Students could tag the resources they find with a predetermined tag, and then the RSS feed for that particular tag could be baked into a live bookmark on the Firefox toolbar. We are currently doing this with a few Furl and del.icio.us feeds set up by our teachers. Adding a tool like Scuttle allows our students to take part in the sharing of resources.