At a Glance
If you're tired of the way your iPod's firmware looks and works, download this open source firmware replacement. Rockbox aims to be more functional and efficient than your iPod's firmware while being easy to use and customizable. Rockbox supports a wider range of sound settings than the iPod's stock firmware, gapless playback, as well as ReplayGain for volume normalization. Users also have access to a wide array of plugins, including games (like a free version of Doom!), fonts, icon sets and theme applications.
Downloading and installing Rockbox can be tricky, so carefully follow the directions and read through all of the documentation. Rockbox has firmware releases for a wide variety of devices, so make sure you download the correct one. Additionally, Rockbox's firmware modifications are highly experimental. Rockbox states that they offer no guarantees that it will not damage your player or void your warranty. The developers state that they've had no issues with Rockbox damaging their players, but you still should download with caution.
Note: This link takes you to the vendor's site, where you can download the version of the software that's best for your PC.