Some Arduinos, eg Leonardo, can act as USB input devices for PCs etc, emulating mice, keyboards etc.

Where the Arduino board does the USB processing on the main chip rather than having a separate USB controller chip, it can be made to emulate USB input devices to a host PC.

• V-USB - a software USB device for Atmel’s AVRs
• Add extra USB port to Arduino
• USB Keyboard/Mouse and using sendReport()
• USB Keyboard HID Usage Tables

• Keyboard emulation
• Keyboard emulation:keyboardmodifiers

• PS2Keyboard Library
• Extension of the original PS2Keyboard library
• Alternate PS2Keyboard Library
• Arduino PS2 Keyboard FULL keyboard protocol support and full keys to integer coding
• Details of the PS2 Keyboard interface
• Instructables PS2 Keyboard to Arduino
• PS2 Keyboard or Mouse

• Dynamic keyboard
• USB Rubber Ducky keyboard mimic device
• USB Rubber Ducky Project Wiki

• Mouse functions
• Joystick Mouse Control
• Arduino/Wiring Library for interfacing with a PS2 mouse

—

• https://github.com/search?p=6&q=arduino+programmable+keyboard&type=Repositories
• https://web.archive.org/web/20110626071011/http://www.usb.org/developers/devclass_docs/Hut1_12v2.pdf
• https://github.com/techpaul/PS2KeyAdvanced/blob/master/src/PS2KeyAdvanced.cpp
• https://github.com/techpaul/PS2KeyAdvancedl
• https://cal-eng.com/?page_id=579
• https://www.instructables.com/id/USB-Pedal-HID-Keyboard-With-Arduino-Leonardo/
• http://www.fourwalledcubicle.com/LUFA.php
• http://mitchtech.net/arduino-usb-hid-keyboard/
• https://hackaday.com/2012/06/29/turning-an-arduino-into-a-usb-keyboard/

If any referenced page no longer exists, try looking for its URL on http://archive.org.