Kapow is a punch clock program designed to easily keep track of your hours, whether you're working on one project or many. Simply clock in and out with the Start/Stop button. If you make a mistake in your hours, you can go back and edit any of the entries by double-clicking on the session in question. Kapow also allows you to easily keep track of the hours since you lasted billed a client, by providing a helpful "Billed" checkbox--the totals will reflect your work after the last billed session.
Install kapow on ubuntu
Open the terminal and run the following commands
sudo apt-add-repository ppa:gottcode/gcppa
sudo apt-get update
sudo apt-get install kapow