History:

The original eReaders (Kindle, nook, sony) Tablets (iPad, Android)...
eReaders allowed you to buy books in digital/electronic form rather than on paper at a discount.

  1998 - Rocket from NuroMedia
  2006 - Sony Reader with e-ink.
  2007  kindle books from Amazon to read on their kindle eReader.
  2009  Barnes & Noble introduces the nook with similar capabilities
  2010  Apple releases the iPad with an e-book app called iBooks
  2011  Samsung releases the Galaxy Tab running the Google Android OS
  
  The basic kindle and nook's use E ink screens to increase contrast and allow reading in
  direct sunlight just like a paper book.  However, both kindle and nook have introduced
  new models with color LCD screens like the iPad and android tablets incorporating email
  and other apps to increase functionality.
iBook - iPad apple.com/ibooks
eBook - Barnes & Noble (Nook app),
Amazon (Kindle app)

File   format
Kindle .azw, .kf8, .txt, .pdf, .mobi, .prc
Kindle fire .azw, .txt, .pdf, .mobi, .prc, aac, mp3, midi, OFF, Wav, MP4, vp8, .doc
Nook   .pdb
iTunes .epub (IDPF)
The .epub or OEBPS format is an open standard for e-books
created by the International Digital Publishing Forum (IDPF).

See Comparison of e-book formats - Wikipedia

You can get books in several different file formats
(some books are available in all formats, others in only 1 or 2.)

pdf - Fixed line length (will not flow text to fit the screen) so you have to scroll yourself.
kindle - Will remember where you were when your checkout expires.
EPUB - Can download directly to tablets or eReaders

See OverDrive-Device Resource Center for others.

	Mac	Windows	iPad	Kindle	Kindle Fire	Nook	Android
Library borrowing OverDrive app
e-Books
	PDF/OPDF	PDF/OPDF				EPUB OEPUB
	EPUB OEPUB	EPUB OEPUB	EPUB OEPUB iBook			EPUB OEPUB	EPUB OEPUB
Audiobooks
Music
Video
Purchased Books/Media
Amazon kindle	a	a	a				a
B&N nook	a	a	a				a
Apple iBook
Apple iTunes					4	4	4
	Mac	Windows	iPad	Kindle	Kindle Fire	Nook	Android
Documents/Media (click on media icon to play a sample)
Web Browser				5
Flash
				?		?
Word Excel PowerPoint MS Office			1	2	2		3

a. Amazon.com: Free Kindle Reading Apps

1. The iPad has iWork apps (Pages, Numbers, Keynote) which read and write MS Office documents.

2. Word documents and other formats (rtf, jpeg, gif, png, bmp) can be converted via e-mail for viewing on the kindle.

3. The Documents to Go app ($15 & free ver.) will read MS Office documents

4. I copied MP3 songs I had ripped and M4As I just bought from the iTunes store and they played. Older iTunes files are DRM (Digital Rights Management) protected and can't be copied.
See Copy iTunes to Droid the Easy Way - YouTube

5. Experimental browser. (search for "webKit" at Amazon's kindle page.)

  Format         Reader
   pdf          Adobe Acrobat (app on most of above devices)
   Adobe EPUB  Adobe Digital Editions (Mac, PC), OverDrive (iPad, Android, )
   Kindle       Kindle Reader - Kindle app for most of devices above 
   (All kindle books are also on EPUB)
   
   pdf has fixed line lengths, so you may have to scroll left and right on a small screen
   EPUB and Kindle will flow text to fit your screen/window
   Other:
   OEPUB - Open EPUB - No DRM (Digital Rights Management), free to copy
   OPDF - Open PDF
   
 On kindle
   Can download directly from Amazon to PC
   Must put in documents directory to kindle
   
 Audiobooks
     MP3 - Mac, iPod, Windows
     WMA - Windows
     AA
     AAX

iPad
Some apps for magazines are in NewsStand.
Stand alone

All OverDrive distributed e-books, audiobooks, music, and video play in a proprietary media player called OverDrive Media Console, while e-books can also be downloaded and played in Adobe Digital Editions software.

Overdrive is the most common software used by libraries for e-books.

Getting Media: Instructions for libraries:

	Somerset Co	Ocean Co1 eLibraryNJ	Overdrive MyHelp 2
iPad
kindle
nook
android
Windows
Mac

1. eLibraryNJ (Listen NJ) includes Scotch Plains, Ocean County, New Jersey State Library and many others.
2. With MyHelp.overdrive you will have to click one of the other tabs then go back to Setup

Where are the files:       
   Windows: C:\users\[std usr]\my documents\my digital editions\xxx.epub
   
       Mac: ~/Documents/Digital Editions/The_Social_Media_Survival_Guide.epub
            ~/Downloads/TheSocialMediaSurvivalGuide.ascm
            ~ = your folder under /Users
      The book: The_Social_Media_Survival_Guide.epub
      It also updates your manifest.xml file with the expiration date and other things.
      
  The overdrive system also creates an .ascm (Adobe Content Server Message File).
 This is adobe's form of rights management.  See ebook-system.
 

OverDrive Media Console: download and shortcut keys Help at Overdrive | Somerset Co Library Nook - Download to PC and transfer to Nook via USB Kindle - USB like Nook or direct from Amazon with Wi-Fi iPad, Android, - Download with overdrive app Mac - Windows: Read with Adobe Digital Additions

ACSM - Adobe rights management. Requires special app which gets book from the Internet.
BlueFire Reader