SoX is the Swiss Army knife of sound processing tools: it can convert sound files between many different file formats and audio devices, and can apply many sound effects and transformations, as well as doing basic analysis and providing input to more capable analysis and plotting tools.
Rosegarden is an audio and MIDI sequencer, score editor, and general-purpose music composition and editing environment. It is an easy-to-learn, attractive application that runs on Linux. It is ideal for composers, musicians, music students, and small studio or home recording environments.
dagrab is a command line driven tool for extracting digital audio from cd. It works great with IDE drives (and others type too if the kernel supports digital audio read for them, I think this does not include SCSI drives for now), and supports jitter correction, filters and audio post-processing,as well as CDDB to automatically name your files appropriately.
cdparanoia reads audio from the CDROM directly as data, with no analog step between, and writes the data to a file or pipe in WAV, AIFC or raw 16 bit linear PCM. Cdparanoia will read correct, rock-solid audio data from inexpensive drives prone to misalignment, frame jitter and loss of streaming during atomic reads. cdparanoia will also read and repair data from CDs that have been damaged in some way.
cdrtools (formerly cdrecord) creates home-burned CDs/DVDs with a CDR/CDRW/DVD/BluRay recorder. It works as a burn engine for several applications. It supports CD/DVD/BD recorders from many different vendors; all SCSI-3/mmc- and ATAPI/mmc-compliant drives should also work. Supported features include IDE/ATAPI, parallel port, and SCSI drives; audio CDs, data CDs, and mixed CDs; full multi-session support; CD-RWs, DVD-R/-RW, DVD+R/+RW, BD-R/BD-RE; and TAO, DAO, RAW, and human-readable error messages. cdrtools includes remote SCSI support and can access local or remote CD/DVD/BD writers.
dave's cd player (dcd) is a simple command-line CD player. It plays CDs, loops (sequences of) tracks, plays tracks at random, and so on. Its a full featured, but simple-to-use CD player. It supports libmusicbrainz (musicbrainz.org) for CD information if desired, yet remains one of the leanest CD players out there.