Wolfram Research, probably most known for their Mathematica calculation product, has launched an online service which makes various calculations and visualizations for free, and with just a web browser:
This project makes me really respect Wolfram. I spent quite some time browsing the examples, almost exclusively from the “mathematics” part, picking like a shy visitor at other areas. Some of my online friends write that “knowledge becomes less of a fashion in our times”. I do not agree a bit. Just look at this product.