Magic Lantern is free software that runs on Canon DSLRs to give them enhanced features with more control for shooting video. It's like custom firmware, but it runs directly from a memory card without altering the camera's software. This video from Jake Coppinger shows how to get started using the powerful tool. It's all pretty simple to get going: First, make sure your camera's firmware is up to date, set the camera to manual mode, clear all your camera settings and format the memory card. Then you can head to the Magic Lantern site and download the software that matches your firmware version exactly. Once you copy it to your SD card, you can put it in your camera, turn it on and navigate to "update firmware". This will cause it to boot the new software. Then you'll be up and running with Magic Lantern. We dove into the software years ago but it's made quite a bit of progress since then, with new tools that will help you focus your picture, monitor audio and shoot timelapes sequences.
Because the software is not from Canon themselves, the developers can't promise that it won't damage your camera, and Coppinger recommends a few precautions. Don't open the memory card or battery door while the camera is powered on, and if you want to remove Magic Lantern, do a full format of the card within the camera rather than just deleting the files. Watch his video for a full rundown of how to get started with Magic Lantern.
Upgrade Your Camera for Free - Getting Started With Magic Lantern [Jake Coppinger via PetaPixel]