Team Monitor
With CTRL ALT DEL you invoke the Team Monitor which lists all currently running programs.
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Programs that were launched by the system are blue, those started by the user black.
Applications that are unresponsive, which is often a sign the program has crashed, are marked red. You can try to quit a program by selecting it and pressing (or either DEL or Q). If that doesn't work, try (or SHIT DEL or K) instead.
You can summon a Terminal with OPT ALT T.
If your Tracker or Deskbar crashed or froze, a new button appears (you may have to kill the offending team first):
will restart Tracker and/or Deskbar for you.