Browser BASIC

Browser BASIC (BBASIC) is a JavaScript application that embeds a BASIC language interpreter in a Web page. BBASIC lets you load, enter, run, and save programs written in a variation of the BASIC language. BBASIC provides sophisticated control structures, includes a wide variety of functions, supports graphics, and offers other features.

You might have to press the Tab key or click the canvas to give it keyboard focus. For Internet Explorer 10 (and probably for other versions of this browser), you will need to clear its cache after saving a file or risk not seeing the file in a subsequent FILES command listing. (Press Ctrl+Shift+Delete to access Internet Explorer 10's Delete Browsing History window.)