As of March 2011, the most popular type of ebook is the one used by Amazon's Kindle. The file format used by Kindle is .azw, and is proprietary software created specifically for use on Amazon's e-reader. The Kindle ebook uses Digital Rights Management (DRM), which prevents unauthorized copying or use of the Amazon-purchased ebooks on non-Kindle software. Amazon has released Kindle applications for devices such as the iPhone/iPad and Google Android, allowing users to purchase and view Amazon ebooks via Whispernet, a framework for delivering Kindle ebooks.
The eReader ebook format is created by Palm Digital Media, a company currently owned by Barnes and Noble. eReader uses the .pdb file format and is a freeware program, meaning it can be used by consumers and as a platform for development by software makers. This flexibility makes eReader ebooks available for many popular digital devices and computers by installing eReader software. In addition, anyone can create eReader ebooks using Dropbook or eBook Studio. eReader books are sold on eReader.com.
EPUB is the ebook format developed by the International Digital Publishing Forum. The format itself is based off the open standards of Open Publication Structure, a variant of HTML, XML and the ZIP compression format. Because these technologies are widely used on the Internet and by computers, the EPUB file format can be used on Kobo eReaders, Apple's iBook app, Barnes and Noble's Nook eReader and several other software and devices.
The Sony Corporation-developed Reader uses a type of ebook known as Broadband Ebooks, or BBEB for short. Broadband ebooks use the .lrf file extension. All BBEB ebooks are published with DRM encryption, which prevents the ebooks from being accessed on non-Sony Reader equipment. According to Steve Haber, Sony Reader president, the company has sold millions of the eReader and was developing an app to work with Apple iOS (iPhone/iPad). In February 2011, the Sony Apple app met with compatibility complications, pushing back the project indefinitely.