“V-USB is a software-only implementation of a low-speed USB device for Atmel’s AVR® microcontrollers, making it possible to build USB hardware with almost any AVR® microcontroller, not requiring any additional chip.”
For further details on V-USB and licensing, visit http://www.obdev.at/products/vusb/index.html
This is a data logger project that reads an analog signal, converts into digital number, and sends it to a host computer using Virtual USB. This is a good example application of V-USB. An 8-pin ATtiny45 microcontroller without an external crystal oscillator is used for this demonstration. The beauty of this project is the ATtiny45 presents itself as a USB keyboard to the host computer, and sends the measurements by itself.
Read more: Easy Data Logger with Virtual USB using ATtiny45 microcontroller