Rockbox
Rockbox is a GPL-compliant open source operating system for MP3 music players (portable digital audio players, or DAPs). Rockbox began in 2002 and was first implemented on the Archos Studio DAP because of owner frustration with severe limitations in the manufacturer-supplied user interface and device operations.
Rockbox can completely replace the host device's operating system firmware and has matured to become an extensible, flexible platform that provides a plug-in architecture for adding PDA functionality, applications, utilities, and games, and has also managed to retrofit video playback functionality onto DAPs first released in mid-2000. Recently, Rockbox added a voice-driven user-interface suitable for operation by blind and visually impaired users, and is being ported to other DAPs, such as those offered by iRiver and more recent Archos devices.