software-recommendation
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What media (music and video) players are there?
Please list one piece of software per answer, as per this meta post.
Déjà Dup is (from Ubuntu 11.10) installed by default. It is a GNOME tool intended for the casual Desktop user that aims to be a "simple backup tool that hides the complexity of doing backups the Right Way".
It is a front end to duplicity that performs incremental backups, where only changes since the prior backup was made are stored. It has options for encrypted and automated backups. It can backup to local folders, Amazon S3, or any server to which Nautilus can connect.
Integration with Nautilus is superb, allowing for the restoration of files deleted from a directory and for the restoration of an old version of an individual file.
Note that as of February 2016 this project appears to be almost completely ignoring bug reports with only minor triage activity and the last bugfix dates back to 2014, though there are new releases with minor changes.
Category: Other
StackApplet is a GNOME panel applet that monitors your activity on any StackExchange site.
stackapplet 
in Ubuntu Software Center
Get the latest version as follows:
sudo add-apt-repository ppa:stackapplet-dev/stackapplet
sudo apt-get update
sudo apt-get install stackapplet
The first time the application is used, run
python /usr/share/stackapplet/stackapplet.py &
from a terminal.
Best Answer
VLC Media Player
(source: hostmar.co)
I was using it the other day to play back 3 720p videos simultaneously on a 1 1/2 year old HP notebook. Performance was flawless.
Very advanced customizations/settings.
Separate window that includes playlist, file browser, external devices and local network access, internet features (radios, postacasts, Freebox TV channels for registered users)
(Using skins reduces the easy access to some of these features.)
VLC media player supports many audio and video compression methods and file formats, including DVD-video, video CD and streaming protocols. It is able to stream over computer network and to transcode multimedia files. (from Wikipedia)
It can use extensions, plugins and skins - to be downloaded from addons.videolan.org.
Among these, some that can find movie subtitles. (More answers on this: here and here.)