I'm looking for software that will allow an audience to collectively formulate and vote-up questions during a presentation which can be relayed back to the speaker either during or after the talk. The goal would be to structure and prioritize questions from a large audience to the speaker, such as during conferences, by members of the audience using laptops and possibly smartphones.
I vaguely remember reading about a tool like this a few years ago that Google employed during their Tech Talks. If I'm not mistaken they had this running on Google App Engine. However I can't remember where I read about this, nor can I find any reference to it now.
Can anyone recommend such a tool that will allow for quick interaction from an audience with the ability to upvote questions?