It is definitely not normal for people to get comped for having their work mentioned in someone else's book. This "comes up" a lot in security[1] because almost everyone serious in the industry winds up writing tools, and there are so many little nooks that it's easy to end up being "the authority" for (e.g.) SCADA protocols or Bluetooth fuzzing or whatever.

Long story short: you're happy about this. Buy the author a bottle of wine to thank them.

[1] scare-quotes applied because I've never seen someone be concerned about it

Yes. Support them as best you can. This will get you better known and will only help you in the end.

Ask to see the the book before it's published, or, if possible, the drafts.

This way you can make suggestions ("Why didn't you include a paragraph or two about feature X?") and correct mistakes ("this bug was fixed in version 1.3.4" or "this feature is available under the Tools menu").

You might even take the feedback from the authors, improve your software and have the book reflect your updated version if you are fast enough. Just beware the feature creep, as always, and don't try to delay or annoy the guy, he's just doing his job too.

This is great marketing for you and the least thing you want is regret the way it was done after it hit the shelves.

Good idea! Thanks everyone for your help.

this is great advice.

I have had a few requests like this over the years. My answer is always "You have my permission to do anything you need to do. I can formalize that in a contract if you require it. What can I do to make this most easy for you?"

(The last time it happened, it was an American state's educational standards committee wanting to write me into their standards document. Why on earth would I say no to that?)

P.S. "Thanks for offering to add me to the acknowledgements. Why don't we save a tree and you can just credit me on the project's website?" (PR7 link for free!)

Remember: the book's users are by definition your users. Your goal is to make them happy. Here's someone else offering to provide them a valuable support resource. This is good news.

Offer to review a draft before publication. You'll catch some of the (inevitable) mistakes, which will make the book better. If it turns out to be a useful book, offer to write a foreword, which will give the book something of an official imprimatur.

If they seem in any way competent and reasonable, and you think they'll do a good job of it (including a reasonable technical review stage, so your product isn't unfairly portrayed as buggy or lacking features it actually has, etc), let them at it. If your product's name or logo are trademarked, however, be sure that they include the relevant trademark notices.

If you are particularly protective of your product's logo, you could refuse to allow general use of it on books without explicit permission (this is true of the Ruby on Rails logo and DHH, for example).

Don't ask for anything. You will be able to use the book as promo, and even link to it on Amazon with your own affiliate.

Beyond money, there are a few opportunities here. For example, maybe the author would see about letting you post his guide to your software on your site. This would be advertising for his book and a learning tool for your users.

Second, you could offer to take a look at the material before he publishes it, make suggestions, etc. This would benefit him because you are a superuser, and it would benefit you because you can make suggestions and help make it the best advertising tool.

Additionally, if you have a new software release coming up, you should offer to give him a beta version and at least let him know about the latest features, since books become outdated very quickly. This may even motivate you to get stuff done!

They are working for free writing a book that essentially boils down to helping give your app additional mindshare on the off chance that the book gives them a decent return on their time.

If there was a bunch of money in writing the book, you probably would have already written the book... and your book would be infinitely if not markedly better since you wrote the app/software.

Nothing wrong with not wanting to document your free software to the point where the book is useless, but asking money from someone that wants to do this for you for free isn't something I would personally recommend.

This is probably a good sign for your app and will improve your "whole product". http://en.wikipedia.org/wiki/Whole_product

I don't know how disruptive your app is, but Geoffrey A. Moore goes into detail on this in his book Crossing the Chasm. He discusses how the support from others(such as this book) boosts your product in the eyes of your customers and future customers.

I think the opportunities that you miss are likely ones we have not thought of.

Perhaps make an offer to do some (paid) work on the book, for example, proof reading, a forward etc.

Maybe highlights of the book should be included free with your software as documentation.

What happens if they never complete the book or publish it? Maybe agree that it goes public domain if that happens, so what is done is not wasted.

I'd say use the exposure to your advantage rather then asking for money (might even turn this opportunity away).

Give the author as much flexibility. Than start developing a premium option in anticipation of the increase in potential users that the book will bring.

If there is any likelihood of the book getting broad distribution, it would be more reasonable if they were asking you to contribute in some way (write a draft, review their drafts, etc).

What kind of software is it? Knowing might elicit better feedback.

It's freeware with a very broad audience but their book is targeting school kids and teachers.

do I smell bingo cards?!

I think No. Because the book can become part of your Marketing plan. More book will be wroten about your book, more people will discover your app

Don't forget to ask for a copy of the book.

s/ask for/offer/;

I think you need to change the way you view this from short term to long term game. If you have a free app that you want people to use and know about, help the guy out as much as you can. Leverage the limelight of your app and yourself for fun and/or profit. Find a way to monetize your free users, just build your reputation and get paid for lots of consulting gigs, or just be happy people appreciate and use your work.

Many people in your situation would beg or pay to have that kind of exposure. Don't be greedy. Give and ye shall receive.