bpython is a fancy interface to the Python interpreter for Unix-like operating systems (I hear it works fine on OS X). It is released under the MIT License.

a nicer python interpreter with autocompletion, etc.
like ipython

js.js is a JavaScript interpreter (which runs in JavaScript) that allows an application to execute a third-party script inside a completely isolated, sandboxed environment. An application can, at runtime, create and interact with the objects, properties, and methods available from within the sandboxed environment, giving it complete control over the third-party script. js.js supports the full range of the JavaScript language, is compatible with major browsers, and is resilient to attacks from malicious scripts.

JsFiddle is a playground for web developers, an online editor for snippets build from HTML, CSS and JavaScript.