gnome-socket-applet

Installation

First, put this somewhere in your .profile or similar:

export GNOME_SOCKET_APPLET_PORT=13525

Installing:

make
sudo make install

Run:

gnome-panel --replace &

You should now be able to add it. To update the text of the applet, simply open a TCP connection using the specified port, write the text and close the socket again.

XMonad

I use the applet with XMonad. I simply have XMonad write it's logs to the socket using the logHook.

writeLog :: String -> IO ()
writeLog message = safely $ do
    port <- getEnv "GNOME_SOCKET_APPLET_PORT"
    addrInfo <- head <$> getAddrInfo Nothing (Just "localhost") (Just port)
    sock <- socket (addrFamily addrInfo) Stream defaultProtocol
    connect sock $ addrAddress addrInfo
    handle <- socketToHandle sock WriteMode
    hPutStr handle message
    hClose handle
  where
    safely x = catch x $ const $ return ()

Then, in your logHook:

myLogHook = dynamicLogWithPP $ defaultPP
    { ppOutput = writeLog
    }