Mixxx is free mixing software for DJs, providing everything needed to create live mixes. It allows you to beatmatch songs and crossfade them together, like you would with turntables and a mixer.

If you’re new to DJing, don’t sweat it. Mixxx runs without any extra hardware, and is a full replacement for a traditional “turntables and mixer” DJ setup.

For experienced DJs, Mixxx offers a wide range of advanced features. The comprehensive MIDI controller and vinyl control support gives you the tactile feel you need for ultimate control of your mixes. To obtain the lowest latency and highest responsiveness, Mixxx uses hardware video acceleration and takes advantage of multi-core CPUs.

Install Mixxx in Ubuntu:

Mixxx has a ppa on launchpad with packages for Ubuntu 10.04 Lucid, 10.10, 11.04, and 11.10.
Run following commands in a terminal window to add the ppa and install latest Mixxx 1.10:

sudo add-apt-repository ppa:mixxx/mixxx
sudo apt-get update
sudo apt-get install mixxx libportaudio2

Mixxx HomePage: http://www.mixxx.org/