Hello world! with NO repetition
Perl 6 (29 28 characters)

This was somewhat annoying, but I finally managed to make a program for this task. Thanks go to the great #perl6 community, for helping me with this task. It took me two hours, hope you enjoy. The output is completely up to specification, including a newline.

say
Q[@A`DO world!]~|&lt;HeLhg&gt;


There are four tokens of interest.


say

This outputs the argument with new line at end. The new line after the command itself is needed as a space replacement.
Q[@A`DO world!]

This is the first string. Q[] is for raw strings (like r"" in Python). It can take any delimiter (or pair of them), in this case []. In this case, I use this for quotes, I don't need raw string behavior.
~|

This is stringwise (~) bitwise or (|) operator.
&lt;HeLhg&gt;

&lt;&gt; is list literal, which takes space separated list of elements. In this case, it has one element, and used as a scalar, it gives a string.