QStopWatch was originally written by Dominic Battre, as a simple but effective stopwatch application. You can use it for timing how long things take, with a very simple interface. Start, stop and clear, what more do you need? At the time, Dominic made his program available (for free, under the GPL) at kde-apps.org. Unfortunately, time has taken its toll on this useful little application, and it no longer works with the current version of PyQt. Therefore I've taken the liberty of updating the script so that it works again, and also updating and improving the display.
All you need to download is this little python file (qstopwatch.py), and save it somewhere on your computer. It should work fine on Linux, Mac or Windows, as long as you already have python, pyqt and Qt5 installed.
There isn't any installation, you just need to download and save the python file.
Screenshot from a Linux system showing the simple GUI
You can probably just double-click this python file to run it, and you'll get the window shown below. If that doesn't work, you may have to change the file properties to make it executable. Or you can run it from the command line with the following:
Note, version 1.1 required the (at that time current) python2.7, qt4 and pyqt4. Currently (as of 2021), this version 1.2 now requires the (at this time current) python3, qt5 and pyqt5.
This basic screenshot shows the stopwatch gui. There are only two buttons, a Start/Stop button and a Clear button. While running, the display just shows seconds, and when stopped it expands to also show the milliseconds, as shown here.
As a bonus, while running the window title shows the time too, so you can also see the running time on your taskbar, if you have one.