Rankforest keeps track of the sales rank metric made available by Amazon.com through their generous and extremely useful web APIs. It also monitors the sales ranks published by Barnes and Noble. Frequently these metrics are of great use to authors, publishers, and analysts. While it's quite difficult to relate the sales rank information directly to sales, it is a useful measure of popularity.
Rankforest began tracking some books and CD's back in 2005. Since then many authors have added their books and used the system to monitor the effectiveness of promotional campaigns and to satisfy a curiosity of market reception.
As of July 2009, nearly 8 million individual rankings had been collected for 4,668 items submitted by 3,473 authors and publishers..
Rankforest is user-driven. Many of the sites features come as a result of feedback from individual users. Please don't hesitate to contact me if there's something you want to see.
I've been developing software for the last 10 years and live in Atlanta with my wife and miniature schnauzer. I love books and helping authors. Rankforest has been available to authors and publishers for a few years now, with no major issues or downtime. Many of the features found on other sales rank tracking sites are based on Rankforest. I keep things running so you can see how your book is selling.