Rockbox is an open source firmware for mp3 players that allows you to do many things with your player that the manufacturer doesn't support or allow. For example, I have an 80GB iPod Video. I also have lots and lots of digial music files, mainly in FLAC. My problem was that Apple does not support playback of FLAC files in iTunes or on iPods. Enter Rockbox. This alternate firmware (AKA iPod operating system) allows for the playback of FLAC files along with a plethora of other formats. Rockbox also frees my iPod from the death-grip of iTunes, which I find to be bloated, slow, and limiting software. Many other players are supported, including Archos, Cowon, Toshiba and Sandisk. I've been using it for about 2 years now, and it's just phenomenal. It plays video and pictures, and even records audio. It also comes with lots of games, has every hardware/software EQ, setting, and option you could think of, and is skinnable, meaning the player and its menus can look however you want them to. If you have an iPod or other supported player and you have music Apple doesn't support, or you just hate Apple but love the iPod, then Rockbox is for you.