OpenKeyfreeze is a free Windows application to block your keyboard input without "locking" the screen. Useful for cat owners especially :)
It is a system tray icon only. Play icon indicates keyboard input is active; stop sign indicates the keyboard input is blocked.
The source code is less than 5000 characters, feel free to read it over!
It has no interface besides the system tray icon. To close the program, you can close it thru Task Manager.
You can open "Other system tray icons" (in Taskbar Settings) to make it always shown, like in the screenshot below. Then you can put the exe (or a shortcut to it) in C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
to run it on startup.