repl.it - Online REPL for over fifteen languages

REPL.it is an interesting project from Amjad Masad and Max Shawabkeh that provides an in-browser Read Eval Print Loop (REPL) for over fifteen languages:

The site provides a list of examples for each language that you can load directly into a REPL to execute and inspect results. Check out the source on GitHub to see how it works or contribute your favorite language.