In keeping with the Brainfuck style, I made this interpreter extremely terse and difficult to understand. It's composed of 20 lines of Ruby code and was made as a sort of 'code golf' challenge to myself.
Brainfucker.load("
++++++++++[>+++++++>++++++++++>+++>++++<
<<<-]>++.>+.+++++++..+++.>>++++.<++.<+++
+++++.--------.+++.------.--------.>+.
")
Hello, world!=> nil