Microsoft Word shows you your documents exactly as they'll appear on the printed page. But it doesn't tell you how those documents got that way. That may not sound important, but if you're fixing up someone else's messy formatting (or even your own messy formatting), it can mean a lot. For instance, is that word in all caps because someone entered the Font dialog box and clicked "All caps?" Did they assign a character style to it? Or did they simply type it with the Caps Lock on?
If you're reformatting the document yourself, knowing the answers to those questions will make the job easier. CrossEyes shows you this information at a glance. In Word 2007, you'll find the CrossEyes button on the Add-Ins ribbon; in Word 2003, it's on its own CrossEyes toolbar. Either way, when you click it, a pane opens up at the bottom of the menu which displays the text and--rather than the formatting itself--the commands that define it. It's bit like examining color-coded HTML, only less cryptic. You can easily see why Word displays that text that way, making it easier to change it.
Options allow you to abbreviate long patches of text without formatting changes, and control what formatting CrossEyes displays.
As I write this, version 5.0.1 is in public beta. The beta version will support Windows 7 and Word 2010.