Actually, if it is a strong enough hardware, you can run any GUI application that you'd like with vnc (like I do Ktorrent and aMule on my headless Arch server).
Here's how you do it:

QBittorrent is one of the best torrent clients available that runs on the Raspberry Pi's ARM hardware. It sports both a desktop client and an easy to use web interface. One of the best parts of qBittorrent is its powerful web interface that allows you to control almost every aspect of the client with relative ease. Torrentflux is available in the Ubuntu repositories, but I think in a quite outdated version now. Deluge can be obtained from the getdeb repositories. It also has a GUI client software that you could run from your desktop and connect to the 'headless client' running on your server to control it.

1. Install basic xorg, a basic window manager and tight vnc on the headless server:

2. Run the server once so it will create ~/.vnc and setup passwords

Ubuntu Headless Server

3. Setup the vnc startup script (so you wont need to ssh and manually activate it after the headless reboots).
Call it vnc and put it in /etc/rc.d/
Dont forget to set it up to run at startup in rc.conf
replace daf666 with your username!

#!/bin/bash

# general config
. /etc/rc.conf
. /etc/rc.d/functions

case '$1' in
start)
stat_busy 'Starting vncserver'
su daf666 -c '/usr/bin/vncserver'
if [ $? -gt 0 ]; then
stat_fail
else
add_daemon vnc
stat_done
fi
;;
stop)
stat_busy 'Stopping vncserver'
killall Xvnc
if [ $? -gt 0 ]; then
stat_fail
else
rm_daemon vnc
stat_done
fi
;;
restart)
$0 stop
sleep 3
$0 start
;;
*)
echo 'usage: $0 {start|stop|restart}'
esac

Best Torrent Client For Headless Server Download

4. To setup openbox to run at startup insert 'openbox' in your ~/.vnc/xstartup

5. Reboot the headless

6. Install tightvnc on your desktop machine and connect to the headless: vncviewer 6.6.6.6:1 (replace with ur IP and screen num)

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7. X particles 3 5 crack download. Install ktorrent or what ever. then it will keep running after you disconnect