title: Slickest REPL console in any language
body: <p>Many languages of REPL consoles with additional features like autocomplete and intellisense.  For instance, iPython, Mathematica, and PyCrust all make some effort to go beyond a basic read eval loop.  REPLs are particularly useful in languages where interactive exploration is very important, such as Matlab or R.</p>
  
  <p>I'm looking for inspiration.  What application provides the slickest REPL?  Or what features do you always wish existed in your REPL of choice?</p>