Nintendo's new adapter that allows classic GameCube controllers to connect to the Wii U has a new use now that a programmer going by the name "elmassivo" has developed an open source driver that allows a Windows PC to recognize the USB adapter and accept GameCube controller input. Now you can use authentic Nintendo hardware to play your favorite PC games. I haven't tried it for myself (so use at your own risk), but I'm glad to see that exists. Here's some of the README file:
This is a vjoy feeder application written in C# using LibUsbDotNet.
It allows for communication with the WUP-028 model of the Wii U to Gamecube USB adapter.
This driver has been confirmed to work on Windows 7 and Windows 8 so far.
Z-Axis is the L trigger
X-rotation is the C-stick X axis
Y-Rotation is the C-stick Y axis
Z-rotation is the R trigger
When calibrating the triggers, do not make them click (hit the button), it will cause you to go to the next screen and could mess up your calibration.
Rumble is not currently supported.
Input lag is variable as of the 2014-11-28.5 release. It defaults to 10ms (~2/3 a frame) and can go as low as 5ms (roughly 1/3 frame) or as high as 30ms (just under 2 frames). Faster refresh rates (lower values) will use more processing power but be more responsive.
Now you can use a GameCube controller to play Windows versions of classic GameCube games like Resident Evil 4 the way they were meant to be played. I love how the community steps up to fill needs left open by the original hardware producers. I've given my DualShock 4 controller a second role to fill by connecting it to my PC and it's become my primary Steam gaming controller. Find a need a fill it, I say.