More on Hydra. More on the use of Hydra in the “gathered together/logged in together” pattern, among conference goers at Apple's WWDC conference:
However, those with a clue– of which I got one on Wednesday– used Hydra to take live, collaborative, notes during the various sessions. Someone in the session would start an ad-hoc Hydra network and publish a document. Anyone else interested in doing so could collaboratively edit the document.
End result; you would have up to about a half dozen or so developers asking questions about the presentation, answering each other's questions, and building upon the ideas within the session.