Being mentioned in the same sentence as Max Ernst is an honour! He always was a man I admired very much. One of my favourite works of his is this painting in the museum in Ålborg, Denmark. I was never quite sure why I like it so much. It is called, Bonjour Satanas.
Their site is here: Krita and you should be able to just go to the download tab and get a working copy. It is open source.