This is an equation editor which is not as good as LaTeX but generates HTML instead of images, which I think is way cooler.
Most of these equations have been designed to be copy-paste compatible with Word and Outlook (except the square root, i cbf to fix that... if you think you have some HTML that looks good cross-browser and in Word/Outlook, let me know).
I think this is cross-browser (you just need a Unicode font installed - Arial Unicode MS is preferred because integral signs look so much more awesome).