GitBook can generate your book in different ebook formats.
This is the default format. It generates a complete interactive static website.
Portable Document Format (PDF) is a file format used to present documents in a manner independent of application software, hardware, and operating systems.
It's a very common format. Files have the extension .pdf.
EPUB (short for electronic publication; sometimes styled ePub) is a free and open e-book standard by the International Digital Publishing Forum (IDPF). Files have the extension .epub.
ePubs are supported by Apple and Google devices.
The Mobipocket e-book format is based on the Open eBook standard using XHTML and can include JavaScript and frames. It is supported by Amazon devices (Kindle).