Kimai is a free open source timetracker. It tracks work time and prints out a summary of your activities on demand. Yearly, monthly, daily, by customer, by project, by action ...
Kimai does not have to run to do the recording. You can even quit your browser. Your time is still recording until you stop it from any web browser that has access to your installment. It is designed to hold lots of users but you can use it for a single user if you need to.