What is Rockbox? Why should I use it?
Rockbox is an open source firmware replacement for a growing number of digital audio players. It has been in development since 2001 and receives new features, tweaks and fixes every day to provide you with the best possible music listening experience. Rockbox aims to be considerably more functional and efficient than your device's stock firmware while remaining easy to use and customizable. We believe that you should never need to go through a series of menus for an action you perform frequently. We also believe that you should be able to configure almost anything about Rockbox you could want, pertaining to functionality. It is written by users, for users.
Another top priority of Rockbox is audio playback quality. Rockbox, for most models, includes a wider range of sound settings than that device's original firmware. A lot of work has been put into making Rockbox sound the best it can, and improvements are constantly being made. All models have access to a large number of plugins, including many games, applications, and graphical demos.
You can load different configurations quickly for different purposes (e.g. a large font for in your car, different sound settings for at home). You can even customize your While Playing screen to display only and exactly what you want to see when your music is playing. In addition, Rockbox features a wide range of languages, and all supported models also have the ability to talk to you - menus can be voiced and filenames spelled out or spoken.source: http://www.rockbox.org/