Quod Libet is a music library management program. Rather than categorize songs by genre, artist, and album, it lets you search and display them however you want. It supports regexp-based searches, album cover display, tag editing, ReplayGain, multimedia keys, and an OSD. Also included is Ex Falso, a tag editor that has the same editing features found in Quod Libet, but does not play audio files.
Goggles Music Manager is a music collection manager and player that automatically categorizes Ogg Vorbis, FLAC, MP3, MP4, ASF, and Musepack files based on genre, artist, album, and song. It supports gapless playback, features easy tag editing, and allows scrobbling tracks to last-fm.
ReOrganize4L is a tool for rearranging the files on an MP3 stick. It is based on ReOrganize! for Windows and supports many devices. The main idea behind it is that most MP3 sticks sort the tracks by date. ReOrganize4L first copies the tracks to a temporary directory on your hard drive, then rearranges the order of the files. After this, it copies the tracks (with the new order) back to the stick.
libkarma is a C library for managing the Rio Karma via TCP/IP. It supports all basic protocol commands and some advanced functions on top of these, like caching of the Rio database. There are two proof-of-concept tools included, riocp and chprop. riocp can be used to upload files to the Karma.