The HIDUINO project provides firmwares, documentation, and example code for building a class-compliant USB-MIDI device from an Arduino UNO or Mega 2560. HIDUINO does not use middleware software to convert serial messages through a MIDI loopback port (like LoopBe1 on Windows or IAC on OSX). Instead, HIDUINO provides a true USB-MIDI device for plug-and-play compatibility on Windows, OSX, and Linux - just like a commercial MIDI controller. HIDUINO takes advantage of Arduino boards where a second AVR chip is used as the USB controller, so it won't work with single chip variants (e.g. Leonardo), nor older boards that use an FTDI chip as USB controller (e.g. Duemilanove). Many cheap Arduino knockoffs that pretend to be an Uno or Mega also might not work, since they tend to use the (slighly) cheaper FTDI chips.