The GNOME panel lets you add lots of applets and small apps and run on your desktop without leaving space.
Timer applet is one of these apps. This lets you configure one or a few countdowns and open it whenever you want in your taskbar.
You can select as many calculations as you want with the timer applet and select the one you want to select.
During each countdown, the ID and the look can be configured, the specified notification options that end after the count.