What's a "gnusb" ?
The gnusb is a platform for building USB controllers - like mixers, foot pedals and the like - primarily for use with Max/MSP or pure-data.
It's name stands for: "gnu": open source like in gnu/linux and "usb": "usb sensor board"
The gnusb is a real chameleon and can become a variety of things, thanks to V-USB, a virtual usb driver from objective development
It can become an USBasp AVR programmer, a HID-Class device like the Videobass or the Videostick, a custom class device with it's own driver and MaxMSP external like my virtual mixing console, or an Arduino compatible MIDI-Device like the Midignusbuino
gnusb meets Arduino!
The gnusb can now be Arduino-compatible and programmed from within the Arduino IDE
Introducing the Gnusbuino
The Gnusbuino is an adaption of Michael Egger's gnusb that is (more or less) compatible with the Arduino environment. It uses the V-USB virtual USB driver from obdev.at instead of a dedicated USB chip (FTDI on the Arduino) - is thus a lot easier and cheaper to build oneself - very few components, single sided PCB… It has a bootloader and can programmed directly through USB. It can mimic many devices (like the USBasp AVR programmer or a standard USB-MIDI interface).
A variant of the Gnusbuino called Midignusbuino is a sort of Arduino that enumerates as a standard MIDI-Class device that connects directly through USB and doesn't need any drivers, interfaces or software hacks
And then there is the Babygnusbuino: A ridiculously small Arduino with USB interface for bootloading and/or MIDI connection, based on the gnusb / Gnusbuino project. Really bare-bones, no protection, no FTDI chip, single-sided PCB, no holes. The USB connector is directly etched on the board, so you actually plug in the PCB itself to upload a new sketch to the Arduino.