KaTeX is a math formatting library for web pages. It is much faster than MathJax 2, but supports far fewer features. The main thing I want to format is matrices. They added support for this in June 2015.
This is the LaTeX-formatted math:
k.renderToString("\\begin{bmatrix} x \\\\ y \\end{bmatrix} = size \\times \\begin{bmatrix} \\sqrt{3} & \\sqrt{3}/2 \\\\ 0 & \\tfrac{3}{2} \\end{bmatrix} \\times \\begin{bmatrix} q \\\\ r \\end{bmatrix}", {displayMode:true})
Client-side
This is rendered in the browser:
Server-side
This is rendered on the server and turned into html. This does not require the 147k javascript library to be loaded, but it does need the css and fonts.