Typing Stats is an add-on designed to help you improve your typing skills and, thus, your productivity. The add-on shows statistics about your typing speed and accuracy and even which fingers made the most mistakes.
Typing Stats runs in the background while you type in the browser (eg, typing up emails or a Google Doc). Its analysis is pretty comprehensive, with data on how many keystrokes you type correctly per minute, how many characters you correct using the backspace per minute, your total typing time, and the characters you've had to correct the most. If you're a start-and-stop-again type of typist, the "histogram of intervals between keystrokes" will show you that.
All of this data can help you become better at typing by showing you want you need to work on. (I seem to constantly correct the "n" key, for example, thanks to my error-prone pointy finger on my right hand.)
Although the tool lets you display different intervals for the analysis (last 24 hours or last week, for example), it would be better if it showed a smaller interval, like the last hour — in case you want to do a typing test rather than see all your typing over time.
Still, faster and more accurate typing will catapult you, hopefully, into the productivity big leagues and Typing Stats is one useful tool to help you get there.