At hystry I try to improve the odds of good conversation online. I have built several prototypes exploring two key mechanisms for conversation: highlighting updates to pages you visited, and notifying you when people reply to your comments anywhere in the blogosphere.
The most recent prototype performs sophisticated parsing to create a smarter RSS-like browser for the entrepreneur forum Hacker News. Read all about it in this slidecast.
My first website, I put this together to be notified when people replied to my comments anywhere in the blogosphere, and so improve my odds of good conversation.
I spent maybe a week working on it over the last couple of months before I graduated, in between writing up my PhD dissertation and rehearsing my defense, and then while on vacation in India.
It never quite scratched my itch, but it helped me find something better.