DJ Mixing Software provides instant bpm beat matching, synchronised sampler, scratch, automatic seamless loops and remixing functions, effects, and much more...
Mixxx is free, open source DJ software that gives you everything you need to perform live mixes.
KraMixer DJ Software
Kramixer is a free DJ software program that runs on most versions of Windows.
UltraMixer is a DJ-Mixing-Software which enables you to mix digital music in various formats such as MP3, WMA, OGG, WAV or CDs in real time. All you need is a sound card. The DJ's turntables are replaced by two digital SoundPlayers.