The 16FUSB is a software implementation of the USB low-speed for PIC16F628/628A microcontroller. All communication stuff is done by the firmware, completely discarding the need to use an additional chip. From the 16FUSB core is possible to add implementations of other protocols such as, for example, I2C, SPI or simple write data from the USB host (PC) directly to the PIC pins.
This project have as inspiration a similar design for Atmel AVR microcontrollers: The IgorPlugUSB by Igor Cesko.