Drawing Tablets & Input (Drivers & Low-level Hardware): open-source projects that exist because someone reverse engineered a closed product, sorted by GitHub stars.
Patched Wacom drivers for old Bamboo, Intuos and Cintiq tablets on modern macOS
Low-latency Windows graphics tablet driver for Wacom, Huion, XP-Pen and others
Firmware collection for Silead touchscreen controllers, extracted from Windows drivers for Linux
Linux PIDFF force feedback driver with fixes for Moza, Simagic and other wheelbases
DKMS package of the hid-nintendo driver for Joy-Con and Switch Pro controllers
Linux app to download drawings from Wacom SmartPad devices over a reverse engineered BLE protocol
Linux kernel driver for VEIKK graphics tablets
Saitek X52/X52 Pro joystick MFD and LED driver and mapping software for Linux
Linux driver for TourBox controllers over USB and Bluetooth, with haptics and GUI config
GNU/Linux replacement for the Wacom Inkling SketchManager
USB bridge for serial and ADB Wacom and other legacy pen tablets
Linux kernel support for the Logitech G923 steering wheel
Mac OS X driver for Wacom serial tablets and TabletPC digitizers
Diagnostic tools for UC-Logic (Huion, XP-Pen, Gaomon) graphics tablets
Send images and text to the Wacom Intuos 4 button OLEDs on Linux
JavaScript library for Wacom STU signature pads over WebHID