Dj Techtools Midifighter Classic
The default Mixxx mapping has the buttons mapped to hotcues 1-8 for decks 1 & 2.
This controller has been discontinued. A similar product, the DJ TechTools MIDI Fighter 3D, is still available from DJ TechTools and includes a 3D motion sensor.
This is the Mixxx Wiki - 
Mixxx is a free and open-source DJ software.
Manual
Hardware Compatibility
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Contribution Guidelines
Coding Guidelines
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Developer Guide
Creating Skins
Contributing Mappings
Mixxx Controls
MIDI Scripting
Components JS
HID Scripting