Question: The Hubstaff icon is not showing in my system tray (I’m using Ubuntu).
Answer: Not all systems support system tray icons – namely, Gnome and Unity based desktops. They have removed the system/tray icons as they have decided it is not something they want any longer: http://design.canonical.com/2010/04/notification-area/
Depending on what Linux environment it is, you can add in a package to get it back as they haven’t removed them entirely, they are just not installed by default. Others have removed it entirely (such as Ubuntu, mentioned above) and the user needs to find an alternative “third party” (e.g. not maintained / released with the desktop) implementation of the system tray.
We are working on adding Ubuntu specific code to the Hubstaff app so it will show in the system tray even though this feature has been removed, so that will be available in the future.