Magic Lantern is an open platform firmware for the Canon 5d Mark II created by Trammell Hudson that enhances the video features of the camera.
Magic Lantern is an enhancement atop of Canon’s firmware that makes your 5D Mark II into the 5D Mark Free. It adds new features like onscreen audio meters and zebra stripes, as well as disables the audio AGC. It is an open (GPL) framework for developing extensions to the official software, tailored for film making needs.
Thanks to David Vandervoort for the tip!