If you've ever worked with an old-school tracker, Renoise will look instantly familiar. Music is made in grid-based patterns, and these patterns can be arranged to create songs. It might look and sound like quite a techy workflow, but for a lot of people, it works.
Of course, this kind of interface isn't going to appeal to everyone, but if you do buy into the tracker philosophy, you'll find that Renoise implements it superbly. It comes with its own audio processors and supports plugins; it's OS X, Windows and Linux-compatible; and you can ReWire it to other DAWs.
Version 3 has brought a completely rebuilt GUI and a whole load of new features; it is, without doubt, the most powerful tracker in existence. 5 Stars
FULL REVIEW: Renoise 3.0