dudl is a collection of tools to grab, encode, and rename MP3 files, archive them, and maintain a database of all files. On top of this runs the dudld Jukebox daemon that plays your files through gstreamer. dudld's strengths are the powerful tag based filters, the capability to cope with very large collections, and the network protocol to control its operation. There is a full featured command-line client, a minimalistic GTK client, and a lirc client. Writing new clients should be easy with the supplied client libraries.
OpenDJMix is a virtual DJ system which allows you to mix MP3 files and audio CD tracks. It consists of a C++ API that manages a virtual sound bus with its I/O and a Qt GUI that enables a user to mix 4 MP3 or audio CD tracks. The API has been designed to be used in all multitrack sound tools.
SvOlli's Little Audio Related Thingies, or SLART for short, is a compilation of rather simple programs that are related to audio files: it consists of a player (Partyman), a CD ripper, a tag editor, and some other tools. These programs can communicate with each other via a custom IPC bus, so a newly ripped track can be automatically queued in the player, for example.
K-Yamo is an MP3 and Ogg Vorbis tagger with ID3v2 support. It can store ID3v1, ID3v2.3, or ID3v2.4 tags. It also stores pictures in the tags. K-Yamo supports multi-file editing. It can guess tags out of filenames, and fetches the missing parts from musicbrainz. It also cleans up your files into a structured filesystem tree which makes use of the tags in the files. Finally, it is a CD ripper with FreeDB support. A MySQL database can optionally be used for tagging.
FUPlayer is a full featured music manager and player for the GNOME desktop. With it, you can play music from your hard drive, create playlists, do real file management using its Trash, and play, rip, and burn audio CDs. It features an interface similar to those of many modern manager-style players, but with many improvements, such as true non-modal search and browse functionality, find-as-you-type, and drag destination highlighting. It aims to be extremely user friendly and efficient to use.
Cactus is an audio player. It shows all your music files in a kind of database, and you can easily browse, edit, and search your collection. It also supports synchronizing your music collection with a mobile player device. It plays MP3, WAV, and Ogg. It can also import and rip audio CDs, automatically show album covers, tag MP3 files, and maintain a fast library. A GTK 1.x binary is also available.
The FAAC project includes the AAC encoder FAAC and decoder FAAD2. It supports several MPEG-4 object types (LC, Main, LTP, HE AAC, PS) and file formats (ADTS AAC, raw AAC, MP4), multichannel and gapless en/decoding as well as MP4 metadata tags. The codecs are compatible with standard-compliant audio applications using one or more of these profiles.