CoRank is a site which lets you create your own social bookmarking sites, which are hosted at yoursite.corank.com – a similar kind of thing to what Ning does with social networks.
This is a great way for small groups to share information through weblinks between each other, without going to the trouble and expense of setting up something like Pligg on a server.
I’ve set up a CoRank at http://virtualcommunities.corank.com/ – feel free to join it and have a play. I’ll still be using del.icio.us as my main bookmark repository though.