Software to show typed keys on the screen
For Linux check Screenkey: https://launchpad.net/screenkey
On Windows there is Carnac the Magnificent.
A keyboard logging and presentation utility for presentations, screencasts, and to help you become a better keyboard user.
Install via Chocolatey:
choco install carnac
Or Scoop:
scoop install carnac
Source on GitHub:
https://github.com/Code52/carnac