How can I force close RescueTime if the icon is gone or unresponsive?

Windows

Open Task Manager by right clicking your task bar and selecting Start >Task Manager. Click the Processes tab and look for "RescueTime.exe" in the list. Select it and choose End Process either by using the button on the bottom right of the window or by right-clicking the process name and selecting End Process from the menu.

Mac

In your Applications folder select Utilities > Activity Monitor. You will see a list of running programs and applications. Look for RescueTime, select it and click the Force a process to quit (X button), at the top of the page. 

Note: At this point, you should be able to unmount any RescueTime installer image, and/or remove the RescueTime application from the Applications folder without any trouble.