Well, I don't know how many people would use it, but I would love to see a decent covert-channel communications system (IRC over ARP?), suitably encrypted. Perhaps we take a poll on suggestions?
It's not quite as useful as dynamo, but uses similar tech so you should be able to key onto it pretty quickly. I have to confess I used a similar idea a few years ago to write a multicast-based instant messaging system (in that instant it was communicate by absolutely any means possible). It's kind of stupid, but is good for both user interface design, security (if that's one of your college focus'), as well as being a bit left field (how many people wrote a port scanner to get passed first year java programming?).