x10mp3 is a plugin for XMMS to control it using X10's Mp3Remote, which comes with Mp3Anywhere, Mp3Anywhere 2000, or DVDAnywhere. It has all the functionality of X10's BOOM2000 software for Windows, plus other handy features like muting, skipping around inside tracks, and balance control.
stream-db is a database-enabled version of streamcast, an MP3 file streamer for icecast/shoutcast servers. stream-db uses a database for the backend instead of perl data structures. The database holds song information, play queues, event logs and request logs. The aim the project is to allow people to create their own streaming media stations, with users, requests, song histories, and playlists and other such fun things.
SmartPlay is a Perl/GTK-based mpg123 frontend with a pseudo-artificial intelligence. Its user interface is very efficent, and it tries to learn from your past listening patterns in order to predict what you want to hear. Both the user interface and AI are designed to minimize the amount of time you spend skipping songs you are not in the mood to hear.