TeX is the gold standard for typesetting of mathematical content. MathLive provides a JavaScript implementation that faithfully reproduces the output of TeX. MathLive supports over 800 TeX commands. (from the product's site)
AxMath is an interactive WYSIWYG equation editor. It enables you to type formulas faster than handwriting. It has all kinds of functionalities which make you type equations at lightspeed. Key features include semantic math input, auto calculation, LaTeX conversion, memory board, etc. It currently supports Win7/8/10 and Office 2010-2016.