alltray 0.71b-1.1 (amd64 binary) in ubuntu cosmic

 With AllTray you can dock any application with no native tray icon
 (like Evolution, Thunderbird, Terminals) into the system tray.
 A high-light feature is that a click on the "close" button
 will minimize back to system tray. It works well with GNOME,
 KDE, Xfce 4*, Fluxbox* and WindowMaker*.
 (*) No drag 'n drop support. Enable with "-nm" option.