Braille is a family of writing systems for the blind, in many languages. The Braille symbols consist of six or eight raised dots each, in two columns. Both sets are included in Unicode. The Braille symbols are not an alphabet in themselves, but can be mapped to many different alphabets in different ways. Different countries commonly use different mappings even for the same alphabet.
Six-dot braille has 64 possible combinations, including blank. This is ample for a single-case Latin alphabet, ten digits, various punctuation symbols, and several other symbols, including some used to mark abbreviations or change encoding modes. By changing modes, one can also change to a different encoding. For example, music written in Braille can be included within text. However, it is impractical to try to squeeze both upper and lower case into a six-dot Braille encoding. Eight-dot Braille has 256 combinations, just like 8-bit bytes on computers, and can therefore map to any 8-bit character encoding directly.
Braille input into a computer can be done by touch typing normally but displaying the input material in a Braille font. There are also special-purpose six-key and eight-key Braille input devices where each symbol is entered by pressing the keys for its dots simultaneously. There are Braille output devices of several kinds, including embossers to create traditional raised Braille dots on heavy paper, and interactive displays that raise pins to create the dots for reading.
Unfortunately Braille hardware is still rather expensive. Braille publishing is heavily subsidized by societies for the blind, and by some governments.
Perkins Brailler owned by Kalibo Elementary School
A possible XO-1 pilot school site
There is a list of Unicode Braille fonts on WAZU JAPAN's Gallery of Unicode Fonts page.
... and the OLPC Project
It is also possible to easily manufacture a transparent Keyboard overlay with raised dots, lines, and arrows etc. for blind children to learn how to use a(any) computer and also several text to speech programs can be found on the internet. File:Braille Keyboard overlay.svg
But at this point in time it is not a primary goal of the OLPC Team to provide this optional item to those governments in concern.