MathJax - display LaTeX in a browser

MathJax is a powerful tool to display latex based mathematical code in almost all web browsers. For example the continued fraction expression of and $e$ and $\pi$ can be easily displayed as Stopping at one point gives some of the most famous fraction approximations of $\pi$, e.g. the two approximations Note that these examples are not pictures, but copyable text (try right click)! One can copy them to e.g. LaTeX or Mathematica.
MathJax is really powerful. Even more fancier examples like commutative diagrams are possible (here: part of the unit laws in a monoidal category) To display commutative diagrams with MathJax use an Xy-pic compatible extension called XyJax. With this extension we can display really fancy pictures like labeled knots. And something I really appreciate: it is possible to display higher morphisms like cobordisms.