You can use Adobe Digital Editions (ADE) with the following screen readers:

Windows – JAWS: http://www.freedomscientific.com/jaws/

Windows – NVDA: http://www.nvda-project.org/

Macintosh – VoiceOver: http://www.apple.com/accessibility/voiceover 

This is a selection of quality resources which may be of use to you. It is not a comprehensive list of free ebooks available online.

Ebook formats will differ according to the ebook provider, however ebooks are generally available as either PDF or ePUB files. 

PDF ebooks have a fixed layout and do not adapt well to different size screens.  As a result PDF ebooks can be difficult to read on devices with smaller screens such as tablets and smartphones.

ePUB ebooks however are able to adapt to match the size of the device’s screen, regardless of the device.  Therefore it is easier to read ePUB ebooks on mobile devices.

Some ebook providers have begun to produce their own apps for offline reading of ebooks on mobile devices.  There are a number of benefits to using the provider's own app for accessing their ebooks rather than Bluefire Reader, such as additional functionality, however the main disadvantage is that you can only view eBooks from that specific provider. 

Knovel ToGo Access downloaded Knovel titles offline for up to 30 days on a mobile device. Note you will need to set up a My Knovel profile to be able to use this app. For more information regarding the app, including how to use it go to the Knovel ToGo Support site.