If you don’t currently have an e-reader, you can download one for your computer (and most smartphones) for free.
Calibre reads most types of e-book files: .epub, .mobi (Kindle), and .pdf — and if you’re creating your own e-books, it will convert the files for you.
Adobe Digital Editions for PC and Mac will read Epub and PDF files.
Kindle Readers are for Amazon Kindle e-books (.mobi) only:
Mobipocket has readers for Windows PC, Blackberry, Palm OS, and other mobile devices.
Barnes and Noble’s Nook application works with PC, Mac, iPhone, iPad, Android, and other devices.
There are many more e-reader applications out there… these are just the main ones.