Quoting its official website, BRLTTY is a background process (daemon) which provides access to the Linux/Unix console (when in text mode) for a blind person using a refreshable braille display. It drives the braille display, and provides complete screen review functionality. Some speech capability has also been incorporated.
Thanks to a powerful API developed with the program itself and its bindings for some programming languages, BRLTTY can also be leveraged by other assistive technologies to provide support for Braille displays (i.e. input and output) without worrying about the “nasty details” of the process, abstracting many of the complexities that are involved.
BRLTTY can also be run in Microsoft Windows, although the process to make it work is not exactly straightforward.