The Ardwiino Guitar Configurator tool allows you to program Arduinos for your own custom controllers.

Features

Controllers can emulate a variety of different controllers, including XInput, PS3, Nintendo Wii Rockband Controllers, PS4/PS5 Rockband Controllers and even a Nintendo Switch Pro Controller
Controllers can either take input from to Wii controllers, take input from to PS2 controllers or the inputs can be wired directly to the Arduino
Controllers poll at <1ms, but due to the limitations of USB 2.0, this will result in a poll rate of 1ms
Controllers support having LEDs react to inputs, including using APA102s (Dotstar) or just wiring regular LEDs inline with the buttons.
An Arduino Pro Micro, Arduino Micro, Arduino Leonardo, Arduino Uno or Arduino Mega can be used.
Tool is cross platform, with LED support working on Linux, macOS and Windows.
Star Power tilt support for Guitar Hero Guitars with mercury switches or other tilt switches

Note

Avoid using USB 2.0 hubs when using these controllers, they poll so quickly that multiple guitars on a single hub will be slowed down, and some hubs will even cause issues with the controller being detected. However, USB 3.0 hubs are okay, and I have previously used multiple guitars on a single USB 3.0 hub with no issues.

X360 Support

You can use UsbdSecPatch to patch out the authentication checks on an RGH modded console, and then you can use an Ardwiino controller on X360.

Instructions:

Mod your console and install dashlaunch
Copy the xex file from above to your console
Add it as a plugin to dashlaunch
Unplugin your controller, and plug it in AFTER the boot animation.

PS2 Support

You can use the latest build of OpenPS2Loader to allow using PS3 guitars on a modded PS2. If you enable PADEMU it should recognise your guitar and allow you to play games, as long as you have your guitar configured for PS3 mode. Both PS3 GH and RB guitars are supported.