Reverse-ish a string!
Pyth, 1 byte
X

Verify all the test cases.
Pyth has wonderful built-ins :-)

Pyth,  8  7 bytes
sm@_QxQ

Verify all the test cases.
How it works
This is the more interesting non-built-in approach.
sm@_QxQ  - Full program.

 m       - Map over the input.
  @_Q    - Get the index in the reversed input.
     xQ  - Of the first index of each character in the String.
s        - Join the list.