Typora - A minimal Markdown reading & writing app.
MarsEdit - MarsEdit is a desktop blog editing application for the Mac. It provides an offline interface to most popular blogging systems. WordPress, Blogger, Tumblr, Movable Type, and many other systems are supported.
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
BlogDesk - Blogging should be simple, but it gets complicated and time-consuming if you are serious about it.
MarkText.app - Mark Text is a Markdown editor for Mac, Windows and Linux.
Open Live Writer - Open Live Writer makes it easy to write, preview, and post to your blog.