Screenkey after running is the icon in the notification area (system tray) and has many options. Supports multiple monitors, can be placed on a screen over the Windows of any app and in any place (provided slop/slop-opengl).
Screenkey can display the usual keys and key combinations, you can customize the font and color of fields displayed, the display time (latency), and various other... Screenkey was initially a modification (fork) project of the same name abandoned in version 0.2, was later almost completely rewritten, with bug fixes and adding new features.
-Several keyboard translation methods
-Key composition/input method support
-Highlighting of recent keystrokes
-Improved backspace processing
-Normal/Emacs/Mac caps modes
-Dynamic recording control by pressing both control keys
-Switch for visible shift and modifier sequences only
-Countless bug fixes
Installation latest version into Linux Mint:
sudo apt install python-gtk2 python-setuptools python-setuptools-git python-distutils-extra
Download and unpack
cd /tmp; wget https://github.com/wavexx/screenkey/archive/master.zip; unzip master.zip; cd screenkey-master
sudo ./setup.py install
If you like, add a program in startup