Arduino Leonardo Screen Locker BadUSB
Are you tired of your colleagues because they never lock their workstations when they leave their desks? Just get an ATMEGA32U4, make your cross-platform keyboard-like locker device and teach them a lesson!
You can get one for 5-6$ with a really sophisticated case like this:
Build and upload this little piece of code to your device with Arduino IDE You will need for Keyboard.h also, but Arduino IDE can handle it.
This code was tested on Windows, Linux and OS X.
Plug it in the back of their device and let the fun begin! 10-20 times locked screen later they will remember to always lock their machine.