Is there a mixing program that exist for mixing mp3/wav files like for example VirtualDJ or Tracktor for Linux Ubuntu?
Yes. Try Mixxx (http://www.mixxx.org/).
I have used Mixxx on several radio gigs and at home. Works great and stable even after hours of mixing.
Audacity is a multi-track audio editor for Linux/Unix, MacOS and Windows. It is designed for easy recording, playing and editing of digital audio. Audacity features digital effects and spectrum analysis tools. Editing is very fast and provides unlimited undo/redo.
Supported file formats include Ogg Vorbis, MP2, MP3, WAV, AIFF, and AU.1
For more information on Audacity, check out the Audacity web site.
To install Audacity, just click on the image below.