repl.it – that’s REPL as in Read-Eval-Print-Loop – is a neat online project which allows users to play around with various programming language interpreters directly from their browser.

Each language runs in an interpreter build on top of JavaScript, and the interpreters run entirely client-side in the browser’s JavaScript environment.¬†repl.it currently supports 16 languages, including Ruby, Python, Scheme, JavaScript, Lua, some old favorites like QBasic, and even some toy languages like LOLCODE.

The project is open source and all the code is available on GitHub. Many of the interpreters are written using Emscripten, an LLVM bytecode to JavaScript compiler.