This is a very approachable and well presented introductory text on Calculus. It is written with an advanced high school student or beginning college student in mind. It covers all the traditional topics in a calculus curriculum - functions, graphs, limits, derivatives, integration, etc. The material is presented in a very straightforward manner and it is very easy to follow. There are multiple worked-out examples throughout the text, and each section ends with a several problems and their solutions. The problems vary in difficulty, and many are designed with practical applications in mind. The book also emphasizes the use of scientific calculator in working out of many problems, which is pedagogically a good approach. This book is available under the Creative Commons License through the CK-12 foundation, which means it can be reprinted, modified and resold if necessary.
The Kindle formatting of this textbook leaves something to be desired. The book was originally typeset in LaTeX, and this did not translate all that smoothly into the Kindle format. I've found that getting this textbook on other e-readers or computers in the epub format rendered it much more satisfactorily.
This is not the flashiest textbook that you will come across, but in my opinion it gets the job done.