Argos, GNOME Shell extensions
Argos is a free GNOME version of BitBar. Both lets you run any script to create an icon in the panel (or Mac OS X Menu Bar). You can see lots of plugins here: BitBar plugins.
This screenshot shows the hosts file, opened from the argos extension. The extension is shown as a notebook icon with the number of unknown entries.
It complains on forgotten entries in your `/etc/hosts` file. See Argos-hosts for more info.