The system tray

CardTray lives in the tray. Closing the main window hides it there: CardTray keeps running, and any game you had open stays saved exactly where you left it. Click the tray icon to bring the window back.

While today's Daily Challenge is still unplayed, the tray icon carries a small Daily badge.

The menu

• Continue last game — reopens your most recent game in progress, right where you left it. Greyed out when no game is in progress.
• Today's Daily Challenge — opens the Daily Challenge. See Daily Challenge.
• Open CardTray — brings the window back.
• Share idle bandwidth — a checkbox mirroring the Settings switch. Under it, a line reads Utilities available or Utilities disabled while sharing is off. See How CardTray is funded.
• Settings… — opens the CardTray window.
• Check for updates…
• Quit CardTray — asks first, then exits properly. Quitting stops the bandwidth sharing that keeps the app free, and CardTray can't keep itself up to date while closed.

What usually goes wrong

I closed it and it is still running. Closing the window is not quitting. Use Quit CardTray on the tray menu.

The Massive agent is still there after I quit. It is a separate agent with its own tray icon, and it keeps running while you are signed in to Windows. Uninstalling CardTray stops and removes it.