Audacity is a cross-platform multitrack audio editor. It allows you to record sounds directly or to import Ogg, WAV, AIFF, AU, IRCAM, or MP3 files. It features a few simple effects, all of the editing features you should need, and unlimited undo. The audio I/O uses PortAudio, which fully supports OSS, Mac OS X CoreAudio, and Windows WMME, and can be compiled with support for ALSA and Jack.
Skype uses P2P (peer-to-peer) technology to provide voice- and video-based communication with other Internet users. The technology is extremely advanced, but easy to use. It features excellent sound quality, end-to-end encryption, and automatic negotiation of firewalls or routers. Among major features are SkypeOut and SkypeIn, adding the possibility to make low-cost calls to land line phones and having a fixed number to be able to receive calls from land line phones.
Linphone is an audio and video Internet phone with GTK+ and console interfaces. It uses the SIP protocol, and is compatible with most SIP clients and gateways. It can use various audio and video codecs such as Speex, GSM, G711, G722, ilbc, amr, Theora, H263-1998, MPEG4, H264, VP8, and snow.
Music Player Daemon (MPD) is a server that allows remote access for playing music in various formats and managing playlists. It makes a great desktop player with frontend options (Qt, GTK, ncurses, Windows, and Web clients are available). It is also appropriate as a console player that is scriptable, and is especially useful if X is restarted frequently. A set of rapid development tools for clients are being developed and include a C library, Python module, PHP class, Perl module, and Java Class. The goals are to be easy to install and use, to have minimal resource requirements, to be stable and flexible, and easy to interface.
GLAME (GNU/Linux Audio Mechanics) is meant to be the GIMP of audio processing. It is designed to be a powerful, fast, stable, and easily extensible sound editor for Linux and compatible systems. It has full support for non-destructive editing including undo/redo and applying LADSPA effects. Its supported platforms are Linux, BSD, IRIX, and OS X. It uses guile and libxml, and the GNOME libs available is highly recommended. MP3 and Ogg files can be processed if libmad and libvorbisfile are installed.
Asunder is a graphical audio CD ripper and encoder for Linux. You can use it to save tracks from an audio CD as WAV, MP3, Ogg, FLAC, Opus, WavPack, Musepack, AAC, or Monkey's Audio files. It has CDDB support and can create M3U playlists. It's independent of any desktop environment. It can rip and encode at the same time. It aims to make CD ripping as quick and easy as possible.
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.
MOC (music on console) is a console audio player with a simple ncurses interface in playmp3list style. It supports MP3 (with ID3 tag, VBR, and Xing headers), Ogg, FLAC, WAVE, Musepack, Speex, WMA, MP4, AAC, and some other less popular audio formats. Playlists can be saved and loaded using .m3u files (PLS version 2 can also be loaded). Internet streams (Shoutcast, Icecast) are supported. It achieves gapless playback by employing an output buffer in a separate thread and file pre-caching. The key mapping can be fully customized. The interface can be detached from the server as it plays in the background.
DarkIce is a live audio streamer. It records audio from an audio interface (e.g. a sound card), encodes it, and sends it to a streaming server. DarkIce can record from OSS audio devices, ALSA audio devices, Solaris audio interfaces, and Jack sources. DarkIce can encode into MP3, MP2, Ogg Vorbis, and AAC formats, and can send the encoded stream to ShoutCast, IceCast 1.3.x and 2.x, and the Darwin Streaming Server.
mpg321 is a Free clone of mpg123, a command-line MP3 player. It is designed to be a drop-in replacement for mpg123, and therefore its interface has been designed around that of mpg123, without using any of its code. mpg321 has been designed for use with frontends such as gqmpeg, although it is just as useful on the command-line. Unlike mpg123, it supports ESD and ALSA output without recompiling, and it does all MP3 decoding with only fixed-point math by using the mad MPEG audio decoder library.