This is a Modern Skin for Winamp 5.666/WACUP that aims to 100% emulate what Winamp 1.00 looked and felt like back in the day.
It's as simple as doing a git clone into your Winamp/WACUP skins folder.
Alternatively you can also click on "Code" -> "Download ZIP" and drag the "winamp1-main" folder from the winamp1-main.zip archive into your Winamp/WACUP skins folder.
Feel free to report any issues you find or submit PRs if you think areas of code could be improved.