Here's an overview of projects concerned with implementing reliable multicasting in a scalable manner.
Updates are again most welcome.
Nonhierarchical solutions Most of the nonhierarchical solutions aim at reducing feedback by suppressing negative acknowledgements when noticing someone else is also sending feedback to the sender. Hierarchical solutions are all based on exploiting a tree rooted at the sender, and making the intermediate nodes responsible for aggregating feedback messages. Again, the goal is to reduce the number of feedback messages at the sender.