This extension integrates Ubuntu AppIndicators and KStatusNotifierItems
(KDE's blessed successor of the systray) into GNOME Shell. Including 
support for legacy tray icons.

Features:
  - Show indicator icons in the panel.
  - Reveal indicator menus upon click.
  - Double clicking an icon will activate the application window (if 
    implemented by the indicator).
  - Legacy tray icons
  - Middle mouse click an icon to send a 'SecondaryActivate' event to 
    the application. Support needs to be implemented in the application