Easy
From Esolang
Easy is an esoteric programming language based on Brainfuck. Unlike most programming languages, all actual code-writing is done at runtime, hence the author's joke that "it is extremely easy to write programs in Easy".
The instructions are mostly the same as those in Brainfuck (actually, input and output are switched), but with an added instruction, :, which lets you add code to the end of the program. The : itself cannot be added to a program, and there is always only one, at the end of the program.
: supplies the only way to end a program: if you type anything that is not a valid Brainfuck instruction (: is not considered valid), the program ends immediately.
[edit] Hello world example
The same as in Brainfuck:
>+++++++++[<++++++++>-]<.>+++++++[<++++>-]<+.+++++++..+++.>>>++++++++[<++++>-] <.>>>++++++++++[<+++++++++>-]<---.<<<<.+++.------.--------.>>+.
Note that, of course, this is not actual "source code" but rather the input to the program which will produce the output "Hello World!"
