This is a blueprints for an AR-15 Scratch-Built Receiver. It was created by a man that goes by [email protected] and the PDF links to a geocities page as well as a photo sharing site – both are defunct.
That is a shame, because this looks like an awesome project. The level of detain in the readme is enough for a handy person to be able to build their own AR-15 lower from plate stock.
I am really fond of making your own 0% lower for your own personal use if you have the capabilities. I tried to do it using cast plastic, but it did not work too well.
AR-15 Scratch-Built Receiver Blueprint