Microsoft's Silverlight has support for IP Multicast. This doesn't mean it can multicast, it just means it can join broadcast groups on the LAN, which were originally conceived to be routed in IP Multicast distribution trees worldwide, but are generally blocked out by ISPs or WAN routers for reasons of scalability or policy.

There are no known PSYC projects using Silverlight. There's however a client in .net/C#. See also Flash.