A JavaScript REPL: http://tech.einaregilsson.com/repl.html
A PHP REPL developed at Facebook: http://www.phpsh.org/
A Python REPL: http://www.trypython.org/
A Ruby REPL: http://tryruby.org/
A Haskell REPL: http://tryhaskell.org/
An R REPL: http://rstudio.org/
