NVDA (Non Visual Desktop Access) is a free, open source screen reader that effectively enables blind and visually impaired people to use a personal computer (be it a desktop or a laptop) that runs the Microsoft Windows operating system: it does so by providing feedback via synthetic speech and Braille. It is very lightweight, free to use both in personal and professional environments, highly customizable and extensible via a rich variety of add-ons developed by the community. Additional voices to improve speech quality can be installed separately; of course, NVDA also provides support for Braille displays.
NVDA can be leveraged to effectively test and evaluate the accessibility of an application or web page via a screen reader. While this could feel intimidating at first, a guide to use NVDA for accessibility testing by webAIM is available; the NVDA User Manual can help as well, as it illustrates in detail all NVDA’s features.