GameRanger has six million users, tens of thousands to hundreds of thousands of whom will be active simultaneously. His chat problem involved has moderate fan-out.
Scott Kevill does it on a single machine (last time I checked) with hand-rolled C++ and close attention to the details of how the Linux networking stack works.
Scott Kevill does it on a single machine (last time I checked) with hand-rolled C++ and close attention to the details of how the Linux networking stack works.