Digital Audio Access Protocol (DAAP)
DAAP is a protocol to share media in a network. It was first used in the program iTunes, but is widely used today.
On Debian-based distributions like Ubuntu you can install a DAAP-server using
sudo apt-get install mt-daapd
This will install the Firefly-DAAP-server. You can configure it using the webinterface by opening the page http://localhost:3689/index.html . The default password is mt-daapd; the user field stays empty.