Hamster
Hamster helps you to keep track of how much time you spend on various
activities during the day. Whenever you move from one task to another, you can change your current activity, or you can record time spent afterwards.
Main app: hamster-time-tracker (Ubuntu 20.04 and later) hamster-applet (Ubuntu 18.04 and earlier)
To install hamster-time-tracker in Ubuntu 20.04 and later open the terminal and type:
sudo apt install hamster-time-tracker
Appindicator: hamster-indicator
To install hamster-indicator in Ubuntu 16.04 and earlier open the terminal and type:
sudo apt install hamster-indicator
I've grown fond of Hamster, and used it for tracking how long I worked on a Summer of Code project. It's added to your indicator menus (or systray). When you want to start/stop/change tasks, just hit Super+H and type what you are doing.
It makes some pretty nice statistics for you that can be exported as HTML, for sending to others. You can categorize parts of a job into groups to keep track of what exactly you're doing at the time.
Each task is labelled as [task]@[job]. For example, you could have dev@project, doc@project, etc. Hamster will do some auto-completion on these as well so most of the time you only need to type a few characters. Tags can be added to tasks as well for further categorization.
Screenshot by Toms Bauģis