I know it's not exactly the same, but, open the Javascript developer console in a browser, and you have a somewhat similar capabilities at your fingertips. You

I know it's not exactly the same, but, open the Javascript developer console in a browser, and you have a somewhat similar capabilities at your fingertips. You can alter your whole environment if you consider the particular webpage you're visiting to be your whole environment. You don't need to do much more special for "cos" there either, just type Math.cos(2) / 2. And if you're using Linux, it's easy to be welcomed by the bash prompt of course (and I hear Mac uses a Unix terminal too now these days).