Self

'Hello, World!\n' print.

Repeating endlessly:

[ 'Hello, World!\n' print ] loop.

As a GUI element:

(desktop w hands at: 0) attach: (labelMorph copy label: 'Hello, World!').

Explanation of the above:
    * 'w' gets the last "world" (usually, an X-window)
      in the list of worlds that make up the Self GUI desktop.
    * 'hands at: 0' gets the first 'hand' (cursor) in the given world.
      (Self windows can be on multiple displays, and so can have multiple
      simultaneous cursors.)
    * '(labelMorph copy label: 'Hello, World!')' produces a label object
      with the appropriate text.
    * 'attach:' attaches the label to the cursor, so that the user ends up
      with the label object in his "hand".

    --Jon