If you write in Markdown on your Mac, then you should buy Brett Terpstra’s Marked 2. It could be described as a tool for previewing Markdown files, but that would be like calling an iPhone a… well, a phone.
To be honest, I’ve been using the Marked 2 betas for so long now that I have forgotten what has changed since Marked v1.x. For that, you should take a look at Brett’s blog post that details the changes. I’ll just touch on a few of the biggest changes.
First, Marked integrates with a ton of new apps. As you write in apps like Scrivener or MarsEdit, you can see a live preview of the rendered Markdown in Marked’s window. If you favorite app isn’t supported, you can just drag the file onto Marked’s icon and it’ll update whenever you save.
You can also have Marked watch a folder for changes, and it’ll show you the most-recently update file. This is excellent for me, as I save all my post in the same place, but as it supports nested folders you could conceivably just point it at your Mac’s Documents folder and be done with it.
From there you can run various operations on your text, converting it into pretty much any format your like, including HTML, PDF, DocX and more (you can also add custom output options to the list).
You can also get a crazy amount of information about your text, from visualizing oft-repeated words and phrases, through readability scores to keyword highlighting.
Want more? Sure: you can use custom Markdown engines, or stick with the latest MultiMarkdown (with inline footnotes) [^Like this]; you can use the built-in support for Critic Markup, which is a way to track changes in plain text files, and you can enjoy the brand new icon.
Currently Marked 2 isn’t available in the App store, and there’s no upgrade pricing. The app will cost a mere $12, so you should just go buy it.
Marked 1.x will continue to work, too, and Marked 2 has a free 7-day trial.