Hamster (see: https://github.com/projecthamster/hamster) is a very well know tool for tracking how long you spend working on various tasks/projects. Quote: “Hamster is time tracking for individuals. It helps you to keep track of how much time you have spent during the day on activities you choose to track”.
The Hamster project is busy rewriting their code. Quote: “IMPORTANT Project Hamster is undergoing a period of major transition. Unless someone steps up to the task, this repository will remain unmaintained as the majority of our resources are directed to a rewrite (repositories: hamster-lib/dbus/cli/gtk)”.
It is currently difficult to install Hamster on Ubuntu 18.04 and its flavours, including our own favourite, Ubuntu-Mate.
Here is a method that worked for me.
This method comes from:
https://github.com/projecthamster/hamster/issues/356 (see the post by “dammer”) 
A)
Download python-wnck from:
B)
Download the applet from:
https://launchpadlibrarian.net/202355025/hamster-applet_2.91.3+git20120514.b9fec3e1-1ubuntu2_all.deb
C)
Transfer these debs to a folder of your choice.
Using GDebi install first of all the “python-wnkc” deb, followed by the “applet” deb.
D)
You should see two entries in your menu:
Time Tracker
Time Tracking Overview
I hope this helps Ubuntu-Mate hamster users. 
