Screenkey is a program for Linux that can be used during presentations or webcasts to show the keystrokes you press to the audience, overlaid on top of the applications or systems being demoed. It could be considered the official replacement of the Mouseposé application for macOS.
The installation could not be simpler: just download the package from the website, and follow the instructions. In Fedora, even better: sudo dnf install screenkey
Screenkey is open source, and its development happens in a GitLab project
Warning for Ubuntu users: the version available via apt install screenkey for Ubuntu 20.04 is 0.8, which is old and broken. Thankfully, Ubuntu 22.04 bundles version 1.5.
Another warning, this time for Wayland users in any distro, for example Ubuntu 22.04 or recent Fedora versions: Screenkey still doesn’t play nice with Wayland, and there’s an open issue to track this problem, but there is, thankfully, a workaround; launch it on the command line, setting an environment variable:
$ GDK_BACKEND=x11 screenkey &
With this operation, Screenkey works without problem.