A screen reader is software on various devices that many blind and some low vision people use to access digital content. The screen reader reads out content on the screen and provides feedback as the user uses the device. A screen reader user typically uses the keyboard or unique gestures to navigate, but different users have varying levels of skill related to using various tools and work arounds to manipulate inaccessible content. As a result, there is some variability between users in ability to access content. Screen reading software is different from voice navigation, where the user speaks commands into the device.
Listed above are common screen reader softwares. The testing part of the Digital Accessibility Office at CU Boulder works with all of them to varying extents. Each screen reader has its own strengths and weaknesses, and there is variation in how they work, so it is important to acknowledge those differences. In addition, they are not all available to everyone, and there is at least some learning involved in going from one to another, so it is not appropriate to ask a user to switch screen readers. JAWS and NVDA work on PCs, while VoiceOver works on Macs and iOS devices. TalkBack works on Android devices.
Here is a link to a video of a screen reader demonstration.