Markdown Editors for Mac
I use BBEdit for Markdown Editing, in fact I use BBEdit for just about any text based manipulating, script editing etc. and I regard as an essential "swiss army knife" for my computer.
I know lots of people use TextWrangler but I understand that this is no longer being supported.
We are sunsetting TextWrangler, and we encourage anyone interested in TextWrangler to download and use BBEdit instead.
They also provide a handy chart showing the differences.
If however you only require a Markdown Editor there are plenty to choose from.