MediaTomb is an open source (GPL) UPnP MediaServer with a nice web user interface, it allows you to stream your digital media through your home network and listen to/watch it on a variety of UPnP compatible devices.
So you need a server? Not a web server of course, you rent someone else’s for that. No, you need a file server, print server, intranet, mail server and more. Can free software provide the answer? Of course it can.