This time it is a hardware device. One Bit Groovebox is a synthesizer which produces one bit sound waves. It was created by Noah Vawter (original page is here). The code from the original device was ported to run on AVR Butterfly (with a minor hardware addition), which is a very nice application board from Atmel.
The source code resides in the file OBG-BF.zip. Both hardware addition and the installation process are described in the ReadMe.txt file in the archive. The sounds are the same as in the original One Bit Groovebox device.
If you would like to know somewhat more, go to the software page of the project.