Blu

Here are some of the more robust applications...

Ardour


Record, mix, edit and collaborate.
* Unlimited audio tracks and buses
* Non-destructive, non-linear editing with unlimited undo
* Anything-to-anywhere signal routing
* Unlimited pre- and post-fader plugins
* 32 bit floating point audio path
* Automatic track delay compensation
* Sample accurate automation
* Standard file formats (BWF, WAV, WAV64, AIFF, CAF & more ...)
* Full AudioUnit plugin support on OS X
* More than 200 LADSPA & LV2 plugins freely available
* Support for Windows VST plugins available
* MIDI CC control with 1 click
* Level 2 MIDI Machine Control
* MIDI Timecode (MTC) Master or Slave
* Full integration with all JACK applications
* Video-synced playback, pull up/pull down

(Now for the really good part)
* No copy-protection
* Distributed, world-wide development
* Released under the GPL
* Source code for everyone
* Open XML session file format
* On OS X, works with any CoreAudio supported audio hardware
* On Linux, works with any ALSA/FFADO-supported audio hardware
* Network audio (full fidelity over local network or long haul with CELT) via NetJack

DJ Play

DJPlay aims to be a high class live DJing application for Linux. DJPlay is licensed under GNU GPL

BPM DJ
BpmDj is a program that can be used to DJ. It works under Linux and plays Mp3's/Ogg's. It has a fully automatic BPM counter. It can determine the sound color. It has a full fledged QT based interface. It will help you manage a large amount of songs. Further it can help in creating playlist and has proven to be very robust. The program also allows offline automatic mixing and contains a wavelet based beat graph analyzer to visualize audio tracks.

Final Scratch

Final Scratch is a DJ tool created by the Dutch company N2IT with input from Richie Hawtin (aka Plastikman) and John Acquaviva that allows manipulation and playback of digital audio sources using traditional vinyl and turntables. It seeks to cross the divide between the versatility of digital audio and the tactile control of vinyl turntablism.

* Runs on Mac OS X (10.2.3) and PC/Linux*
* Use turntables and vinyl records to control digital audio files
* FS CD Adaptor Kit** enables use of any CD player as controller
* Plays MP3, WAV, AIFF and Audio CD files
* Assign the same file to both decks simultaneously
* Waveform Display give accurate representation of the music
* Dual color waveform indicates peaks and density of sound
* Track mixing and track organization integrated in one application
* Dynamic Playlist (automatically saves all played tracks in a playlist)
* Integrated BPM detection
* Play Counter and Play Time information for each track
* Pitch readout showing current speed of time code record
* Enhanced sound quality with the support of Traktor FS audio engine
* De-emphasis Modeling for authentic scratching sounds
* Automatic Gain Adjustment (plays all files at same volume)
* Time Code Release Function (continues to play at same pitch without time code)
* Single Controller Mode (control both software decks with a single turntable or CD player)
* Improved Search Function (search 10,000 tracks within seconds)
* Shows waveform in real-time for Audio-CD's
* Variable Font Size
* Adjustable output level
* User customizable keyboard shortcuts
* Mix between FS and analog records or CD's
* Play audio CD's from your computer's CD-ROM drive
* Plays two tracks from one CD simultaneously

MIXXX


* Parallel waveform displays
* Waveform summaries
* MP3, OGG, WAVE, and FLAC playback
* Pitch-independent time stretch (key lock)
* Vinyl emulation
* Wave recording
* Free, open source software
* BPM detection and estimation
* Supported MIDI controllers:

* Hercules DJ Console MK2
* Hercules DJ MP3 Control
* Hercules DJ Console RMX
* Hercules DJ Console Mac Edition
* Mixman DM2
* Tascam US-428
* M-Audio X-Session Pro
* M-Audio Xponent
* Evolution X-Session
* Ecler NUO4
* FaderFox DJ2
* Vestax VCI-100
* Numark Total Control
(and more)

* Multichannel soundcard support (playback and capture)
* Multiple soundcard support
* Cross-platform (Windows XP and Vista, Mac OS X, Linux)
* Adjustable EQ shelves
* Crossfader curve control
* Skinnable interface with extra skins bundled
* Adjustable pitch range
* Multi-core CPU support
* 24-bit/96000 Hz playback and capture
* Crystal clear audio
* Hardware video acceleration
* Vinyl control support for:

* Serato CV02 vinyl
* Traktor Scratch vinyl
* FinalScratch Standard vinyl
* FinalScratch Scratch vinyl
* Serato CD

Terminator X

For those of you who drop by for the first time: terminatorX is a realtime audio synthesizer that allows you to "scratch" on digitally sampled audio data (*.wav, *.au, *.ogg, *.mp3, etc.) the way hiphop-DJs scratch on vinyl records. It features multiple turntables, realtime effects (buit-in as well as LADSPA plugin effects), a sequencer and MIDI interface - all accessible through an easy-to-use gtk+ GUI
* Scratching
* Multiple turntables
* Built-in Sequencer
* MIDI Interface
* Pitch / Volume settings for each turntable
* Effects (Lowpass/Echo) configurable for each turntable
* Syncing tables to one master turntable
* Broad audiofile-type support
* Record to disk
* Save and Load turntable sets (.tX - files)
* Support for LADSPA plugins.
* Support for the JACK Audio Connection Kit
(and more)

Ultramixer Free

* AAC/M4A file support
* Fullscreen and tray mode
* MiniMode Player
* Variable pitch range (up to -/+ 50%)
* Database-driven file archive
* Realtime-BPM Counter
* Support of skinning for the user interface
* Cue points
* 3-Band-Equalizer / EQ-Kill-Buttons
* Import / Export of M3U lists
* FileArchive detail search
* Manual Talkover
* Monitoring over headhones
* Multi-soundcard support
* Automix function
* Switchable fading modes
* Custom fading mode
(the non-free version has a much larger feature list)

More to come...