A python-based real-time spectrum analyzer. Plays MP3s and does FFTs in real time using code from the LightShow Pi project and Numpy.
Full code and instructions at instructables.
Make any USB MIDI Device Wireless with Raspberry Pi
astlab has made a simple device that turns any USB MIDI device into a wireless (WiFi) device that also speaks OSC. They used a USB WiFi dongle to do the transmission. Their target device is aVMeter.