I don't if it qualifies as an actual language, but it is so interesting it does deserve a wiki page. Learn more about it here:

http://cydathria.com/bf/brainfuck.html

http://www.muppetlabs.com/~breadbox/bf/

Also lo and behold the classic "99 Bottles of Beer" written in brainfuck:

http://99-bottles-of-beer.ls-la.net/b.html#Brainfuck