I use Macdown when writing things for my Jekyll[0]-powered website. I've installed the CSS of my website as a MacDown theme, and so I can see what the text would look like when published to the site, in real-time while editing.
In addition I personally have found that while raw Markdown is great for writing, when it comes down to rereading what I wrote and editing it, I prefer a properly typeset version of the text, so I don't have my reading * flow* _broken up_ by [unnecessary characters](http://daringfireball.net/projects/markdown/syntax) and `so on`. And having a live preview lets me reread as soon as I make the change.
It's a minor difference, but I like it. To each his own.
I personally use http://marked2app.com/ for any kind of live preview of websites, or just use the built-in --watch function of Jekyll to automatically generate the site whenever I save a change.
In addition I personally have found that while raw Markdown is great for writing, when it comes down to rereading what I wrote and editing it, I prefer a properly typeset version of the text, so I don't have my reading * flow* _broken up_ by [unnecessary characters](http://daringfireball.net/projects/markdown/syntax) and `so on`. And having a live preview lets me reread as soon as I make the change.
It's a minor difference, but I like it. To each his own.
[0] http://jekyllrb.com/