"Deme, a Platform for Online Deliberation (formerly "POD") is a freely available, open-source web tool for conducting asynchronous meetings that include discussions, document collaboration, polls and voting among small to medium sized groups of people. Our intent in creating Deme (which rhymes with "team") is to support the type of deliberation critical to the functioning of smaller, informal organizations in civil society. Groupspace.org is a hosting site for Deme."
See the site for more, including demos.