TimeTracker

Although monitoring programs don't have any effect on your system or programs' performance, they sure can be very beneficial to users.

TimeTracker is a free, open-source application for Windows that will let you monitor the use of your computer. This is done by compiling data about how much you use the active windows in each session.

Basically, what TimeTracker does is track the time you spend on each open window in your operating system to later display this information and store it for further analysis.

That analysis is, in fact, the most important thing about this application, since it will help you draw conclusions regarding the use you make of your PC, whether you use it for work, leisure, or just to waste time.