Pomodoit

Pomodoro technique allows you to manage your working time by focusing on a task (and only one!) at a time for 25 minutes.

After each work session, you can take a 5 minute break: social networks, email, web, etc...
If you pass 4 sessions in a row, you can take a 20 minute break: nice!

Each session is recorded and you can view the history of your activities.