Golf a string twister
Pyth, 11

jC.&gt;R~hZC.z


Try it here

jC.&gt;R~hZC.z    ##  implicit: .z = list of input split by lines
        C.z    ##  transpose .z to get columns
  .&gt;R~hZ       ##  shift each column by it's index
               ##  equivalent to .e.&gt;bk
jC             ##  transpose back and join by newlines