Impressive. They seem to have added operator overloading to CoffeeScript, among other things:

    # 1. Matrix multiplication

    m1 = matrix([1,  2,  5],
                [2, -1,  6],
                [5, 10, -1])

    m2 = matrix([2,   3,  1],
                [-3, -1, -3],
                [4,   9, -2])

    show m1 * m2

Not sure how this could be used for "serious" number crunching (as it runs in-browser) but I imagine it would be a fantastic teaching tool.