Motivate Clock is a free time manager for Windows.

The program can be very simple to use. Run it in "manual mode", click a button as you switch between work and non-work applications, and it records the basic work/ rest balance for any later reports.

Alternatively, create a "New Project", specify the applications you'll be using for work, and Motivate Clock automatically monitors the current window. When you're using Excel (for example) it adds time to the "Working" clock, switch to a game and it'll add to the "Resting" clock instead.

Run the program over time and a status display lets you see the time you've spent working and resting.

More detailed statistics on offer include the time spent using each individual application.