Name: Anonymous 2016-01-03 20:04
http://codegolf.stackexchange.com/a/68494/48742
Brainfuck, 87 bytes
--->->->>+>+>>+[++++[>+++[>++++>-->+++<<<-]<-]<+++]>>>.>-->-.>..+>++++>+++.+>-->[>-.<<]
The first half initializes the tape to the following:
[0, 0, 0, 72, 36, 102, 108, 111, 108, 90, 33, 45, 0]
The second half transforms this into the string !dlroW , while outputting Hello along the way.
There may have been some brute forcing involved.
Hello, world!, 84 82 bytes
Saved 2 bytes due to Mitch Schwartz.
Small w can be done slightly shorter:
+>---->->+++>++>->+[++++++++[>++++++++>>+++++<<<-]<]>>.+>++>.>..+>>.+>-->--[>-.<<]
These seem to be the shortest solutions ever produced for either variation, at least as far as I can tell.