Root-tail displays a given file anywhere on your X11 root window, i.e. it is
kind of tail -f for multiple files using your desktop background as output
window.

It has configurable colors, fonts, wrapping, justifying, continuation
indicators, geometry, and more and can interleave multiple files also making
it a sort of multi-tail.

For example: 
root-tail -g 800x250+100+50 -font 10x20 /var/log/messages,green \
  -font 12x24 /var/log/secure,red,'ALERT'

By default root-tail doesn't seem to work on XFCE. You need to explicitly 
specify the ID of the display to use it (by using the "-id" flag of root-tail).
Use the xprop command to find the active root display, and run this through
the cut command to strip out the ID number for insertion into the 
root-tail `-id` field.

It looks a little something like this:

root-tail -g 800x250+100+50 -font fixed /var/log/messages,green \
/var/log/secure,red,'ALERT' -id $(xprop -root XFCE_DESKTOP_WINDOW |\
awk '{ print $NF }')
