My non-fiction book needs an index. Is there an app for that?
Yes, and it’s called Word. Most Word users probably have not used it to create an index. Access the index feature (in Word 2013) from the References menu. In the Index sub-menu, use Mark Entry to Alt+Shift+X your way through your document, picking the words you want in the Index. Then, click Insert Index, fiddle with the formatting options, click OK and your Index will appear where you want it. What a time saver! Another great reason to develop your text in Word. For more detail, check this EHow article, which also covers Word 2010.