It's a totally free application that integrates in the status bar. It offers the possibility to start the countdown, stop it or pause it. Its options to assign keyboard shortcuts for these functions will avoid you having to resort to the mouse for these actions.
The software is capable of notifying you when an event occurs by means of different systems, whether a sound alarm, AppleScript notifications or by means of Twitter.
It's also possible to modify the events and manage them from a dedicated window. Likewise, the statistics have their own panel in which you will be able to follow your progress.
Optimizing the time that you spend on your computer is a good way of making the most of its performance and your own. With Pomodoro you'll no longer waste time in front of the screen.