Dillinger.io may not be a good fit for writing your next novel, but it comes in very handy when quickly composing text for the Web. See all Software reviews.
It is not often that I get to review a tool using that same tool, but with Dillinger.io, that's just what I'm doing. Dillinger.io is a text editor, with a twist: It lives on the Web (so, nothing to download), it's free, and it's all about Markdown, an easy way to format your text. See all software downloads.
With Markdown, to produce a bold word, you surround it with double asterisks (like **so**). To make a word into a hyperlink, you surround it with brackets, followed by the link target in parenthesis, producing something that looks like [PCAdvisor](http://www.pcadvisor.co.uk). There are lots of little tricks like this, but not so many as to overwhelm or confuse: The nice thing about Markdown is that you can just focus on what you're trying to say, without fiddling with complex formatting toolbars or numerous arcane tags.
I usually compose my documents in Markdown using WriteMonkey, a minimalistic and powerful full-screen editor for Windows, with word count, segment focus, and other niceties for making writers' lives easier. But one of the few drawbacks of composing a document in Markdown like this is that it's not exactly WYSIWYG: When you italicize a word, you see it surrounded with single asterisks (because that's the syntax for italics), rather than really typed out in italicized letters. When the time comes to render your document to HTML or rich text, you may find formatting that went wrong in surprising ways, and need to go back to your Markdown document to fix things up.
With Dillinger.io, this sort of thing doesn't happen, because Dillinger has a split-screen live view: You type your Markdown on the left side of the window, and watch as the right side fills up with your formatted output in real-time. Seeing your text in double-vision can be disorienting at first: We're very used to seeing letters appear on the screen while typing, but seeing two sets of identical letters appear at once is somehow different. After a short adjustment period, though, I found that the dissonance goes away and it doesn't feel as weird.
Dillinger.io's main draw is the live Markdown rendering. It doesn't have a built-in word count feature (a big minus for me), and there's no spell-checking, either. In fact, even Chrome's built-in spell-checker doesn't work within Dillinger, so you'll have to spell-check outside the browser. On the plus side, Dillinger does have multiple themes, and it's completely devoid of advertising or other promotional annoyances--it just lets you spend some quality time with your text while making sure it still looks right in the end.
If your document is largely composed of simple paragraph text, Dillinger.io may not make a big difference for you. But if you need to produce text for the Web with lots of links and multi-level titles and aren't comfortable with writing raw HTML, it can be very helpful.