Mou was one of the first free markdown tool, promising to be good, with interesting features (as the double panel with markdown on a side and styled text on the other, both syncronised. But it doesn't evolve for months, and in the meantime lot of app come with the same features and more, some in a (beta and temporary) free mode (Typora, Macdown), some become paid (like Write, LightPaper…). There are too many markdown apps to stay quiet such a long time…