Screen Reader enables people with visual impairments access the website. Following is a list of screen reader software freely available over internet that are used popularly.

Non Visual Desktop Access (NVDA) (Windows)
http://www.nvda-project.org/

Orca (Linux GNOME)
http://projects.gnome.org/orca/

VoiceOver (Mac OS)
http://www.apple.com/accessibility/voiceover/