At this point, our only managed offering is the peer channel. The peer channel provides multiparty messaging in a mesh. It is an implementation of the graphing/grouping algorithms in Windows Communication Foundation (WCF), and allows you to use the familiar (assuming you are familiar with the WCF programming model) WCF programming model to send transient messages (think multicast) to the mesh. The messages should be small, because the mesh has a certain amount of redundancy to ensure integrity in the face of node transience. It is very straightforward to use if you are familiar with WCF. If not, there are lots of bloggers on WCF who I'm sure will love to help you out.
We are seeing staggering (from my perspective anyway :)) performance numbers right now, with throughputs of ~1000 messages per second in small meshes...I think it is a bug in our measurements, but we'll know more soon :) However, if the numbers are right, it is a testament to just how performant the stack really is.
If you are planning on using WCF, and are interested in multiparty communication, consider using the peer channel.