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
and
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
And a brainfuck interpreter written in Tcl: