I’d probably have my new app for sale if I wasn’t using it as the subject of my training series. But one of the things that really stuck with me after reading Rework was the concept that you can sell the byproducts of building your product.
In the 37Signals case they sell the books from creating their own product management/development process. I figured, in my case I’d try selling some “how”s in the form of training. One year from now it will be interesting to see if the App or the Training makes more money. 
To put it another way… there’s always a dog under the desk you could sell with your work. Chapter 3 has taken a little longer than I expected, but is almost in the bag.