I recently purchased Harmony Navigator, developed by Cognitone GmbH (located in Germany). It is a really wonderful and innovative product that is a good assistant for me in my composing!
Check out the official videos at: http://www.cognitone.com
How it works? Basically - it can read a .mid file (and if we’re lucky enough Renoise will be upgraded to include .mid export soon, see this thread among others for development progress) that contains a melody and then suggest chords for it. One can also try out compatible chords, sketch new ideas, explore scales and much more.
Don’t miss this tool. Their upcoming product Music Prototyping Studio looks also very interesting…