Open Source Social Networking

I've used Live Journal in my teaching, with varying degrees of success, over the past three years. But I often wished for software that would allow me to create a closed social network without resorting to the whole friends-only approach, which some of my students inevitably failed to mater. Do any of you know about Elgg? It sounds promising, though I probably lack the skills to make it work without technological assistance. I'm wondering, for example, whether it might be possible to run an interactive publication with this sort of software.