What are some alternatives?
When comparing Qtractor and Luppp, you can also consider the following products
Ardour - Record, edit, and mix on Linux, Mac OS X, and Windows.
LMMS - Make music with a free, cross-platform tool
Mixxx - The most powerful free DJ software in the world.
FL Studio - Image-Line's FL Studio, now on it's 12th version, is a well-known music production suite and the most popular beat processor on the market, due no doubt to its longevity. Read more about FL Studio.
Gig Performer - Gig Performer is a cross-platform audio plugin host for live music performances
Logic Pro - Logic Pro lets you translate musical inspiration into professional productions.