The project was called 16FUSB . Software implementation of USB interface with old cheap Microcontrollers like 16F626.
The PIC16F626 is more powerful than PIC16F84A but still is more available and cheaper that Microcontrollers contain built-in USB hardware modules ( such as PIC18F4550 and PIC18F4455).
The project came to be very popular and now is on code.goole.com
The circuit is very simple.
The software on the PIC