Many "consumer electronics" devices that can make use of a house's local network support device and service discovery via a protocol called UPnP (Universal Plug and Play). GUPnP lets GNOME applications discover UPnP devices on the network, and publish services themselves.
DLNA is a set of standards that let devices share multimedia content in standard formats. GUPnP can also perform DLNA-related tasks such as media profile guessing, transcoding to a given profile, etc.
In GNOME, GUPnP is one of the basic building blocks of home-multimedia software like Rygel, a home media server.
GUPnP home page