Noise is the default music player of Elementary OS, built using the GTK3 libraries. Starting with Elementary OS 0.2 Luna, it has been used by default on eOS, replacing BeatBox.
The latest version available is Noise 0.3.1, released a while ago.
Installation instructions:
Noise is available via the Elementary Daily PPA, so installing it on Ubuntu should not cause too many problems. Just add the PPA to your system, update the local repository index and install the noise package. Like this:
$ sudo add-apt-repository ppa:elementary-os/daily
$ sudo apt-get update
$ sudo apt-get install noise
Next, disable the overlay scrollbar for the application:
$ sudo sed -i "s/Exec=noise/Exec=env\ LIBOVERLAY_SCROLLBAR=0\ noise/g" /usr/share/applications/noise.desktop
Optional, to remove noise, do:
$ sudo apt-get remove noise
The installation instructions should work for Ubuntu 15.04 Vivid Vervet, Ubuntu 14.04 Trusty Tahr and derivative systems like Linux Mint 17.2 Rafaela, Linux Mint 17.1 Rebecca, Linux Mint 17 Qiana, Pinguy OS 14.04, Elementary OS 0.3 Freya, Deepin 2014, Peppermint 6, Peppermint 5, LXLE l4.04 and Linux Lite 2.